Based on the statistics presented in earlier discussions, there is controversy with regard to a perceived lack of diversity within the donor sperm pool of many sperm banks. This includes, but is not limited to, height requirements implemented by some sperm banks. [ 13 ]  As a result, it is alleged that potential sperm recipients often encounter very limited sperm donor pool options. Lack of diversity results in very limited choices especially among ethnic minorities within the United States. [ 33 ]  Whenever an individual chooses to specify their preferred donor background, the number of available options (sperm donors that meet the particular individual's criteria) can dwindle down to the low single digits. [ 34 ]  Scott Brown from California Cryobank admitted: "We don't get as many minority applicants as we [would] like." Even after numerous attempts to reach out to numerous ethnic communities, the response can be nearly nonexistent. [ 34 ]


At the California Cryoback, Brown mentions that one out of 100 would be able to become final sperm donor while Ottey from the Fairfax Cryobank mentions one out of 200 would be able to become ultimate sperm donors. [ 35 ] [ 34 ]  In addition, locations of the California Cryobank are in Los Angeles, Los Altos, California; mid-Manhattan, and Cambridge Massachusetts. These locations are known to have a population with higher socioeconomic latitude and being more likely to afford the services. Moreover, one of the requirements includes the potential sperm donor to be able to live nearby the sperm bank in order to provide samples once to twice a month for at least a term of six months. [ 34 ]  This could create potential barriers for populations who are at socioeconomic disadvantage and do not have their own forms of transportation; often having to rely on multiple forms of public transportation to reach certain places. This factor could cause a significant decrease in the sperm donor pool and less diverse availability for sperm recipients.


Some controversy stems from the fact that donors father children for others, in the majority of cases, for single people or same-sex couples, but usually take no part in the upbringing of such children. The issue of sperm banks providing fertility services to single women and coupled lesbians so that they can have their own biological children by a donor is itself often controversial in some jurisdictions, but in many countries where sperm banks operate, this group form the main body of recipients. Donors usually do not have a say in who may be a recipient of their sperm. [ 36 ]


Another controversy centers around the use of sperm posthumously, or after the death of the sperm donor, as pioneered by  California Cryobank . [ 37 ]  Within the United States, there were differences when it came to a child conceived after the father's death and the eligibility for survivor's benefits. Under California law, there was one court case (Vernoff vs. Astrue) in which the mother's child (conceived after the father's death) was not eligible for the survivor's benefits. [ 38 ]  However, Arizona courts had a different approach when it came to children who were born after father's death that the children are eligible for the survivors benefits. There were numerous other stories of similar situations across different states in the United States and even the United Kingdom. Canada, France, Germany, and Sweden do not permit the retrieval use of sperm posthumously. [ 37 ]


Subject to any regulations restricting who can obtain donor sperm, donor sperm is available to all people who, for whatever reason, wish to have a child. These regulations vary significantly across jurisdictions, and some countries do not have any regulations. When an individual finds that they are barred from receiving donor sperm within their jurisdiction, they may travel to another jurisdiction to obtain sperm. Regulations change from time to time. In most jurisdictions, donor sperm is available to an individual if their partner is infertile or where they have a genetic disorder. However, the categories of individuals who may obtain donor sperm is expanding, with its availability to single persons and to same-sex couples becoming more common, and some sperm banks supply fertility centers which specialize in the treatment of such people.


Frozen vials of donor sperm may be shipped by the sperm bank to a recipient's home for self-insemination, or they may be shipped to a fertility clinic or physician for use in fertility treatments. The sperm bank will rely on the recipient woman or medical practitioner to report the outcome of any use of the sperm to the sperm bank. This enables a sperm bank to adhere to any national limits of pregnancy numbers. The sperm bank may also impose its own worldwide limit on numbers.


Sperm is introduced into the recipient by means of  artificial insemination  or by  IVF . The most common technique is conventional artificial insemination which consists of a catheter to put the sperm into the vagina where it is deposited at the entrance to the cervix. In biological terms, this is much the same process as when semen is ejaculated from the penis during sexual intercourse. Owing to its simplicity, this method of insemination is commonly used for home and self inseminations principally by single women and lesbians. Other types of uses include intrauterine insemination ( IUI ) and deep intrauterine artificial insemination where 'washed' sperm must be used. These methods of insemination are most commonly used in fertility centers and clinics mainly because they produce better pregnancy rates than  ICI  insemination especially where the woman has no underlying fertility issues. [ 39 ]


Men may also store their own sperm at a sperm bank for future use particularly where they anticipate traveling to a war zone or having to undergo  chemotherapy  which might damage the testes.


Sperm from a sperm donor may also be used in  surrogacy  arrangements and for creating  embryos  for  embryo donation . Donor sperm may be supplied by the sperm bank directly to the recipient to enable a woman to perform her own  artificial insemination  which can be carried out using a needleless syringe or a cervical cap  conception device . The cervical cap conception device allows the donor semen to be held in place close to the cervix for between six and eight hours to allow fertilization to take place. Alternatively, donor sperm can be supplied by a sperm bank through a registered medical practitioner who will perform an appropriate method of insemination or IVF treatment using the donor sperm in order for the woman to become pregnant.


In the United States, sperm banks maintain lists or catalogs of donors which provide basic information about the donor such as racial origin, skin color, height, weight, color of eyes, and blood group. [ 17 ]  Some of these catalogs are available for browsing on the Internet, while others are made available to patients only when they apply to a sperm bank for treatment. Some sperm banks make additional information about each donor available for an additional fee, and others make additional basic information known to children produced from donors when those children reach the age of 18. Some clinics offer "exclusive donors" whose sperm is used to produce pregnancies for only one recipient woman. How accurate this is, or can be, is not known, and neither is it known whether the information produced by sperm banks, or by the donors themselves, is true. Many sperm banks will, however, carry out whatever checks they can to verify the information they request, such as checking the identity of the donor and contacting his own doctor to verify medical details.


In the United Kingdom, most donors are anonymous at the point of donation and recipients can see only non-identifying information about their donor (height, weight, ethnicity etc.). Donors need to provide identifying information to the clinic and clinics will usually ask the donor's doctor to confirm any medical details they have been given. Donors are asked to provide a pen portrait of themselves which is held by the  HFEA  and can be obtained by the adult conceived from the donation at the age of 18, along with identifying information such as the donor's name and last known address. Known donation is permitted and it is not uncommon for family or friends to donate to a recipient couple.


Qualities that potential recipients typically prefer in donors include the donors being tall, college educated, and with a consistently high sperm count. [ 40 ]
A review came to the result that 68% of donors had given information to the clinical staff regarding physical characteristics and education but only 16% had provided additional information such as hereditary aptitudes and temperament or character. [ 18 ]


Sperm banks make information available about the sperm donors whose donations they hold to enable customers to select the donor whose sperm they wish to use. This information is often available by way of an online catalog. Subscription fees to be able to view the sperm donor through California Cryobank, for example, start at $145. [ 41 ]  This cost could potentially be a barrier for many on limited income and may not have discretionary income to spend on sperm donor services.


A sperm bank will also usually have facilities to help customers to make their choice and they will be able to advise on the suitability of donors for individual donors and their partners.


Where the recipient has a partner, they may prefer to use sperm from a donor whose physical features are similar to those of their partner if they have one. In some cases, the choice of a donor with the correct blood group will be paramount, with particular considerations for the protection of recipients with negative blood groups. If a surrogate is to be used, such as where the customer is not intending to carry the child, considerations about their blood group etc. will also need to be taken into account. Similar considerations will apply where both partners in a lesbian couple intend to have a child using the same donor.


Information made available by a sperm bank will usually include the race, height, weight, blood group, health and eye color of the donor. Sometimes information about the donor's age, family history and educational achievements will also be given. Some sperm banks make a 'personal profile' of a donor available and occasionally more information may be purchased about a donor, either in the form of a DVD or in written form. Catalogs usually state whether samples supplied by a particular donor have already given rise to pregnancies, but this is not necessarily a guide to the fecundity of the sperm since a donor may not have been in the program long enough for any pregnancies to have been recorded. The donor's educational qualification is also taken into account when choosing a donor. [ 21 ]


If an individual intends to have more than one child, they may wish to have the additional child or children by the same donor. Sperm banks will usually advise whether sufficient stocks of sperm are available from a particular donor for subsequent pregnancies, and they normally have facilities available so that the woman may purchase and store additional vials from that donor on payment of an appropriate fee. These will be stored until required for subsequent pregnancies or they may be on-sold if they become surplus to the woman's requirements.


The catalogue will also state whether samples of sperm are available for ICI, IUI, or IVF use.


Some sperm banks enable recipients to  choose the sex  of their child, through methods of  sperm sorting . Although the methods used do not guarantee 100% success, the chances of being able to select the gender of a child are held to be considerably increased. [ 42 ]


One of the processes used is the 'swim up' method, whereby a sperm extender is added to the donor's freshly ejaculated sperm and the test-tube is left to settle. After about half-an-hour, the lighter sperm, containing the male chromosome pair (XY), will have swum to the top, leaving the heavier sperm, containing the female chromosome pair (XX), at the bottom, thus allowing selection and storage according to sex.


The alternative process is the Percoll Method which is similar to the 'swim up' method but involves additionally the centrifuging of the sperm in a similar way to the washing of samples produced for IUI inseminations, or for IVF purposes.


There is a market for vials of processed sperm and for various reasons a sperm bank may sell-on stocks of vials which it holds known as 'onselling'. The costs of screening of donors and storage of frozen donor sperm vials are not insignificant and in practice most sperm banks will try to dispose of all samples from an individual donor. The onselling of sperm therefore enables a sperm bank to maximize the sale and disposal of sperm samples which it has processed. The reasons for onselling may also be where part of, or even the main business of, a particular sperm bank is to process and store sperm rather than to use it in fertility treatments, or where a sperm bank is able to collect and store more sperm than it can use within nationally set limits. In the latter case a sperm bank may onsell sperm from a particular donor for use in another jurisdiction after the number of pregnancies achieved from that donor has reached its national maximum.


Sperm banks may supply other sperm banks or a  fertility clinic  with donor sperm to be used for achieving pregnancies.


Sperm banks may also supply sperm for research or educational purposes.


In the United States, sperm banks are regulated as Human Cell and Tissue or Cell and Tissue Bank Product (HCT/Ps) establishments by the  Food and Drug Administration  (FDA) with new guidelines in effect May 25, 2005. [ 43 ]  Many states also have regulations in addition to those imposed by the FDA, including New York and California.


In the  European Union  a sperm bank must have a license according to the  EU Tissue Directive  which came into effect on April 7, 2006. In the United Kingdom, sperm banks are regulated by the  Human Fertilisation and Embryology Authority .


In countries where sperm banks are allowed to operate, the sperm donor will not usually become the legal father of the children produced from the sperm he donates, but he will be the 'biological father' of such children. In cases of  surrogacy  involving  embryo donation , a form of ' gestational surrogacy ', the 'commissioning mother' or the 'commissioning parents' will not be biologically related to the child and may need to go through an adoption procedure.


As with other forms of  third party reproduction , the use of donor sperm from a sperm bank gives rise to a number of moral, legal, and ethical issues, including, but not limited to the right of the sperm donor remaining anonymous, and the child's right to know their familial background. [ 44 ]


Furthermore, as local regulations reduce the size of the donor pool and, in some cases, exclude entire classes of potential buyers such as single women and lesbian couples, restricting donations to only heterosexual couples who are married. Some customers choose to buy abroad or on the internet, having the samples delivered at home. [ 45 ]


There have been reports of incidents of abuse regarding forced insemination with sperm samples bought online. [ 46 ]


Further abuse of sperm banks comes from the fertility clinic staff themselves. There have been a number of reports of staff at sperm banks and fertility clinics providing their own sperm in place of donor sperm. There have also been cases in which men have claimed their sperm sample was used by a clinic to inseminate a woman without his consent. [ 47 ] [ 48 ]  This has led to cases of malpractice, and in some states, lobbying to create  fertility fraud  laws. [ 49 ]  These incidents have also led to outcry by people who had been conceived by such incidents, raising concerns of consanguinity, as well as the simple right to know who their siblings and biologic parents are. [ 49 ]


Sperm donation laws  vary  by country . Most countries have laws to cover  sperm donations  which, for example, place limits on how many children a sperm donor may give rise to, or which limit or prohibit the use of donor semen after the donor has died, or payment to sperm donors. Other laws may restrict use of donor sperm for  in vitro fertilisation  (IVF) treatment, which may itself be banned or restricted in some way, such as to married heterosexual couples, banning such treatment to single women or lesbian couples. Donated sperm may be used for  insemination  (whether natural or artificial) or as part of IVF treatment. Notwithstanding such laws, informal and private sperm donations take place, which are largely unregulated.


Restrictions on sperm donations or the ability to obtain IVF treatment in some jurisdictions has given rise to women traveling to a country which does not impose restrictions in the circumstances in which they finds themselves to obtain such donations or treatments, in a practice called  fertility tourism .


Most jurisdictions limit the number of children a sperm donor may give rise to. The main reason to limit sperm donations is the risk of accidental  consanguinity  or  inbreeding  between  donor offspring . [ 1 ]  In some countries such limits are voluntary (e.g.,  Japan  and the United States) while in others they are imposed by law, and some jurisdictions do not have any limits. Most jurisdictions which set limits on the number of sperm donations do so in terms of number of donor offspring, but some jurisdictions set the limits in terms of "families", to allow for the children of the recipient woman to be true genetic siblings and because consanguinity issues are caught by a country's  incest laws . Most jurisdictions set only local limits, while a number set worldwide limits. Some jurisdictions permit the export of donor sperms, which may not count in the limit on donor offspring, while the import of donor sperm may be subject to local limits.


Many countries have restrictions on who can be a recipient of donated sperm. Some countries restrict donations to married heterosexual couples (e.g., Japan), and some to married heterosexual or homosexual couples, while others permit donations to married couples or those in cohabitation relationships. In some jurisdictions such as France, single women and lesbian couples have only been able to receive treatments using donor sperm since 2021. [ 2 ]  Some jurisdictions have no restrictions on who can receive donated sperm. In some countries only a husband's sperm can be used for insemination. [ citation needed ]


The rights of the sperm donor also vary. These involve rights to compensation, anonymity, parental rights, child support obligations, besides other issues. Sperm donation by  natural insemination  involves other varied moral and legal issues.


Laws relating to assisted reproduction vary between states. Since 1995, when a child becomes an adult, they can apply for the sperm donor's details. Sperm donors are not paid. Demand is high for donor sperm, and laws vary between states as to how many families a donor's sperm can be provided to. [ 27 ]  In  Victoria , there is a limit of 10 families per donor. [ 28 ]  In  Western Australia , the Human Reproductive Technology Act 1991 (HRT Act) limits the number of families for each donor to 5. [ 6 ]


There is no limit to the number of children born from each donor, however they can only donate to a  maximum of six families. Before the law was changed in July 2007, a medical practitioner could make his or her own decision on the maximum. In the late 1990s  Belgian  fertility clinics (or sperm banks) imported large amounts of donor sperm from other countries and this led to Belgium becoming a ' fertility destination '. However, the Belgian Parliament became concerned about this and, along with the promulgation of the Tissues Directive by the European Commission, the Government decided radically to alter the laws relating to maximum numbers. [ citation needed ]


There is no upper limit to the number of donor offspring in  Canada , but sperm banks generally follow the same recommendations as in the  US , i.e. a maximum of 25 offspring per population of 800,000. [ 9 ]


The  Assisted Human Reproduction Act  banned compensation for sperm donors and imposed a bureaucratic system described as "cumbersome" on donors, after which time more than 90% of donor sperm used in Canada comes from the U.S. [ 29 ] [ 30 ]  The federal government does not track the number of births by sperm or egg donation, and there is no registry. [ 31 ]


In  Denmark , one donor may give rise to 12 children. Before the new limit was set a donor could help to conceive children in up to 25 families who could use the donor sperm for conceiving siblings even after the limit was reached. [ 32 ]


However, Denmark also exports semen worldwide, and where it is the limit of the importing country that is followed, or, when there is no such limit, a fixed amount considering that country's total population, [ 33 ]  in order to minimise the risk of consanguinity.


Through the export it may result in that some single donors have up to 200 biological children worldwide who are genetic half-siblings [ 34 ] .


In  France , donations from a single donor may give rise to six families, but there is no limit to sibling numbers.


The  German  Legislation provides that a donor may not produce more than fifteen children through his donations. The legal position surrounding donations to single mothers and lesbians is still awaiting clarification by the courts. At present a donor can run the risk of paternity proceedings if his donations are used in such cases. [ citation needed ]


In  Israel , sperm donation is mandated by the  Ministry of Health . [ 35 ]  There are 12 authorized sperm banks and hospitals across the country, and 2 more in private research facilities. Only unmarried, healthy men under the age of 30 are allowed to donate sperm, and they are financially compensated for it. [ 36 ]  Men who want to donate must get to the hospital, pass an interview and blood-checks, cryotip and DNA checks. They are also prohibited from donating sperm in more than one sperm bank and they can donate a limited times (usually up to 10 children from one donor). Finally, anonymity is kept indefinitely; the donor would never receive information regarding offspring, and vice versa.


In  New Zealand , a voluntary policy law by fertility clinics limit one donor to "fathering" a maximum of 10 children to four families. [ citation needed ]


Around 1996–97, fertility clinics in New Zealand voluntarily agreed they would only accept donations from non-anonymous donors. [ 37 ]  The Human Assisted Reproductive Technology Act 2004 legislated that all donations made on or after 22 August 2005 must be non-anonymous.


Clinics in  Norway  have a maximum of eight children per donor. [ 20 ]


The law provides that there must not be more than six births per donor. The same law applies to egg donations. Prior to the change in the law in 2008, clinics set their own maximums on the numbers of children produced from each donor.  Spain  was becoming a destination for fertility tourists, i.e. women seeking to become pregnant through the use of donor sperm and Spanish clinics were purchasing donor sperm from other countries in order to satisfy demand (see Onselling in main article). Many UK women were travelling to Spain at that time to be impregnated with sperm imported from clinics in the UK for example, where there were already controls on the numbers of children which each donor could produce.


The change in the law in Spain coincided with Europe-wide discussions on the use and export of human cells.


Sperm donation is only permitted by anonymous donation. Surrogacy is not allowed.


In  Sweden , a donor may give a child to a maximum of six couples. However, each pair may have a sibling in addition. Thus, the limit is 12 children per donor. [ 23 ] [ 38 ]  Nevertheless, the Swedish National Board of Health and Welfare (Socialstyrelsen) recommends a maximum of 6 children per donor. [ 39 ]


Artificial insemination by donor was done only if the woman was married or in registered cohabitation, and required written consent of the spouse or partner. [ 24 ]  This law has now changed allowing single women access to state funded fertility treatment although long waiting lists may prove prohibitive. [ 40 ]


In  Switzerland , sperm donation is only allowed for married couples—not for unmarried couples or singles. A donor may give rise to a maximum of eight children.


The  HFEA  sets a limit of 10 families within the UK which can be created using the gametes of one donor. [ 25 ]  However, there is no limit to the number of children which may be born to each such family from the same donor. A donor may set a lower limit and may impose conditions on the use of his sperm.


Sperm may be exported from the UK but exports are subject to restrictions and have to be notified to the HFEA. Donors must give their permission for export, and normally their donations will not be exported until the 10 family limit within the UK has been reached. In practice this means that only vials from the most fertile donors and those who donate over a longer period of time than the norm, will be exported. Restrictions on exports include ensuring that these are only to approved clinics in any given jurisdiction, and that the use of vials is traceable. Exports to EU states are subject to the EU Tissues Directive which satisfies these criteria. Offspring numbers will thus be limited in each country to which an individual's sperm is exported by the rules in those countries, and UK sperm banks rarely, if ever, impose additional limits. The risk of consanguinity is therefore negligible although some individual donors may produce substantial numbers of offspring if they donate for a long period of time. Because of this, sperm banks operating in the UK tend to limit the length of time for which a man may donate his sperm to six months or a year.


Some clinics exchange vials with clinics in other countries by mutual export and import to enable them to use samples from a wider pool of donors.


The offspring of sperm providers have the right to know the identity of the donor when the person reaches the age of 18, if treatment was in the UK and conception occurred after March 31, 2005. Donors who donated before that time (and after August 1, 1991) can remove their own anonymity. [ 41 ]  Despite fears in the medical profession, the number of donors actually increased after anonymity was removed. [ 42 ]  In 2007, a parliamentary committee recommended that birth certificates include the identity of the donor, but this has not yet been legislated. [ 43 ]


Special permission is required from the HFEA for the export of embryos.


In the  United States , there are few regulations governing who may engage in sperm donation. [ 44 ]  Rather, the  American Society for Reproductive Medicine  and other expert groups (e.g.,  American Association of Tissue Banks ) provide recommendations and guidelines. [ 44 ]  The ASRM guidelines limit a donor to 25 live births per population area of 850,000, [ 26 ]  although this is not enforced by law, there is no central tracking, and it has been estimated that only about 40% of births are reported. It is likely that some donors have over one hundred genetic children. [ 45 ]  Some sperm banks impose lower limits; e.g., the Sperm Bank of California has a limit of ten families per donor, [ 46 ]  and the Rainbow Flag Sperm Bank has a limit of donor children by six different women. [ 47 ]  In 2005, the FDA placed a ban on men who have engaged in sex with another man in the last 5 years being able to donate sperm. [ 48 ]


Spermworld  is an American  documentary  film directed by  Lance Oppenheim  that premiered on  Hulu  and  FX  in the United States on March 29, 2024. [ 1 ]  Spermworld follows the stories of three  sperm donors  and their recipients. Inspired by  Nellie Bowles ' article "The Sperm Kings Have a Problem: Too Much Demand" for the  New York Times , the documentary ventures into "spermworld", the unregulated online marketplaces where sperm donors connect with hopeful parents. [ 2 ] [ 3 ]


Featured personnel in the documentary are credited as themselves (in order of appearance)


The film had its world premiere at  True/False Film Festival  on February 29, 2024. [ 4 ]  It was released in the United States on  FX  on March 29, 2024. [ 5 ]


Straub v. BMT by Todd  was a 1994 case of the  Indiana Supreme Court  which, in a 4–1 decision, ruled that a  custodial parent  cannot bargain away  a child's right to financial support  even with a pre- sexual intercourse   contract . [ 1 ] [ 2 ]  Justice Roger Owen DeBruler dissented, arguing that a transfer of one's child support obligations to another party (assuming that the other party is actually capable of paying the other share of child support in another's place, that is) should be viewed as being permissible just like a transfer of one's liability for negligence through liability insurance is permissible (again, assuming that the other party can actually pay this in another's place). [ 1 ]


In 1986,  elementary school   teachers [ 3 ]  Francine Todd and Edward Straub engaged in a  romantic relationship  with a sexual component. [ 1 ]  In December 1986, Francine Todd informed Edward Straub of her desire to have a child without getting married. [ 1 ]  Edward Straub, who already had five children with his previous wife, was reluctant to  impregnate  Todd, but changed his mind once she threatened to break off their relationship. [ 1 ]  So, Straub and Todd had a pre-sex agreement, in Todd's handwriting, not to seek child support from Straub for any resulting pregnancy, after which point Straub impregnated Todd through sexual intercourse, resulting in the birth of their daughter B.M.T. [ 1 ] [ 3 ]  On January 7, 1991, Todd sued to have Straub be listed as B.M.T.'s father and to force Straub to pay child support for B.M.T. [ 1 ]


In its ruling, the Indiana Supreme Court said that Straub's and Todd's contact was null, void, and unenforceable as a matter of public policy. [ 1 ]  Specifically, it argued that Straub could not have been a  sperm donor  since he reproduced by sexual intercourse rather than by  artificial insemination  and that parents cannot legally bargain away their children's right to financial support. [ 1 ]  This ruling was written by  Chief Justice Shepard  and was joined by Justices  Givan ,  Dickson , and  Sullivan . [ 1 ]


In a short but succinct dissent, Justice Roger Owen DeBruler agreed with the majority that a parent cannot legally bargain away their child's right to financial support  but also  argued that in spite of the fact that one cannot contract away one's liability for  negligence , the government nevertheless allows people to purchase  liability insurance . [ 1 ]  DeBruler pointed out that if people's liability insurance coverage was inadequate, then these people would themselves pay out of pocket, but that it would nevertheless be inappropriate for the  judiciary  to strike down liability insurance by invoking a  public policy  imposing liability for  negligence . [ 1 ]  DeBruler thus argued that if Todd is actually able to pay Straub's share of child support, then she should indeed be legally required to do so considering that she previously agreed and promised to do so. [ 1 ]  DeBruler also invoked Judge Linda Chezem's opinion in this case from the  Indiana Court of Appeals [ 4 ]  in regards to the proper procedure for making certain that B.M.T. receives adequate financial support. [ 1 ]


The  African Journal of Reproductive Health/La Revue Africaine de la Santé Reproductive  is a  peer-reviewed   public health journal  that covers original research on  reproductive health  in Africa. It is published by the  Women's Health and Action Research Center  and the  editor-in-chief  is  Friday Okonofua .


The journal is abstracted and indexed in:


According to the  Journal Citation Reports , the journal has a 2016  impact factor  of 0.700. [ 3 ]


This article about a  journal  on  health  or  health care  is a  stub . You can help Wikipedia by  expanding it .


See tips for writing articles about academic journals . Further suggestions might be found on the article's  talk page .


BMJ Sexual and Reproductive Health  is a quarterly  peer-reviewed   medical journal  covering  reproductive health . It was established in 1974 as the  Journal of Family Planning Doctors  and later renamed  British Journal of Family Planning  and  Journal of Family Planning and Reproductive Health Care  before obtaining its current title.


It is published by  BMJ Group  on behalf of the  Faculty of Sexual and Reproductive Healthcare , of which it is the official journal. The  editor-in-chief  is Sharon Cameron. According to the  Journal Citation Reports , the journal has a 2023  impact factor  of 3.4. [ 1 ]


The  European Journal of Obstetrics & Gynecology and Reproductive Biology  is a monthly  peer-reviewed   medical journal  covering  obstetrics and gynecology  and  reproductive biology . It was originally established as  Nederlandsch Tijdschrift voor Verloskunde en Gynaecologie  in 1889, briefly renaming itself  European Journal of Obstetrics and Gynecology  in 1971, and acquiring its current name in 1972. [ 1 ]  and is published by  Elsevier . The  editor-in-chief  is Janesh K. Gupta ( University of Birmingham ). According to the  Journal Citation Reports , the journal has a 2017  impact factor  of 1.809. [ 2 ]


This article about a  medical journal  is a  stub . You can help Wikipedia by  expanding it .


The  International Journal of Sexual Health  is a  peer-reviewed   academic journal  that covers research on  sexual health  as a state of physical, emotional, mental, and social well-being. It is the official journal of the  World Association for Sexual Health . The  editor-in-chief  is  Eli Coleman  ( University of Minnesota ). [ 1 ]


The journal was established in 1988 under the title  Journal of Psychology & Human Sexuality . [ 2 ]


The  Journal of Reproductive and Infant Psychology  is a  peer-reviewed   medical journal  covering  psychology  as it relates to  human reproduction  and  infancy . It was established in 1983 and is published five times per year by  Routledge  on behalf of the  Society for Reproductive and Infant Psychology , of which it is the official journal. The  editor-in-chief  is Susan Garthus-Niegel ( Technische Universität Dresden ). According to the  Journal Citation Reports , the journal has a 2023  impact factor  of 2.1. [ 1 ]


This article about an  academic journal  on  psychology  is a  stub . You can help Wikipedia by  expanding it .


This article about a  pediatrics   journal  is a  stub . You can help Wikipedia by  expanding it .


Perspectives on Sexual and Reproductive Health  was a bimonthly  peer-reviewed   medical journal  covering  reproductive health . It was established in 1969 as  Family Planning Perspectives , obtaining its current name in 2002. [ 1 ] [ 2 ]  It permanently ceased publication in 2020, alongside the Guttmacher Institute's other journal,  International Perspectives on Sexual and Reproductive Health . [ 3 ]


It was published by  Wiley-Blackwell  on behalf of the  Guttmacher Institute . The final  editor-in-chief  was Dore Hollander. According to the  Journal Citation Reports , the journal has a 2016  impact factor  of 3.571, ranking it 1st out of 26 journals in the category "Demography" and 1st out of 43 journals in the category "Family studies." [ 4 ]


Reproductive Health  is an online-only  open access   medical journal  with a focus on  sexual health . It was established in 2004 and is published continuously by  BioMed Central . The  editors-in-chief  are José M. Belizán (Institute for Clinical Effectiveness and Health Policy) and Sanni Yaya ( University of Ottawa ). According to the  Journal Citation Reports , the journal has a 2018  impact factor  of 2.295. [ 1 ]


This article about a  scientific journal  on  sexuality  is a  stub . You can help Wikipedia by  expanding it .


Seminars in Reproductive Medicine  is a bimonthly  peer-reviewed   medical   review journal  covering the field of  reproductive medicine . It was established in 1983 as  Seminars in Reproductive Endocrinology , obtaining its current name in 2000. It is published by  Thieme Medical Publishers  and the  editors-in-chief  are Richard S. Legro and James Segars. According to the  Journal Citation Reports , the journal has a 2018  impact factor  of 2.585. [ 1 ]


Sexual and Reproductive Health Matters (SRHM) , formerly  Reproductive Health Matters (RHM) , [ 1 ]  is an organisation that promotes  sexual and reproductive health and rights  (SRHR) globally. SRHM's mission [ 2 ]  is to advance the creation and dissemination of sexual and reproductive health knowledge that is grounded in human rights and based on credible evidence, and to facilitate the transformation of such knowledge into action for improved SRHR. This mission is shaped by the understanding that rights- and evidence-based knowledge is power.


SRHM is the only global organisation linked to a scientific, highly reputed journal in the field of sexual and reproductive health that provides an independent voice, has a long-time, trusted reputation, and offers space to a truly global network of researchers, policy makers, programme managers, lawyers and activists in the field of sexual and reproductive health.


The SRHM journal, established in 1993, [ 3 ]  is an  open-access ,  peer-reviewed   academic journal . Founding director and editor Marge Berer, led  RHM  (in 2019, Reproductive Health Matters changed its name to Sexual and Reproductive Health Matters [ 4 ] ) since its inception until 2015 when she handed over responsibilities to Shirin Heidari. In 2018, Shirin handed over her responsibilities to Dr. Julia Hussein as editor-in-chief and Eszter Kismodi as chief executive. In 2020, after Julia announced her retirement, Dr. Emma Pitchforth took over the role of executive editor.


The journal has a 2021 impact factor of 5.732.


Sexual Health  is a bimonthly  peer-reviewed   academic journal  covering the fields of  sexual  and  reproductive health  research, including  HIV , sexually transmitted infections, sexuality, sexual satisfaction, and related topics. It is the official journal of the  International Union against Sexually Transmitted Infections , Asia-Pacific, and the  Asia-Oceania Federation of Sexology . The  editors-in-chief  are Jason Ong and  Joseph D. Tucker . [ 1 ]


Sexual arousal  (also known as  sexual excitement ) describes the  physiological  and  psychological  responses in preparation for  sexual intercourse  or when exposed to  sexual stimuli . A number of physiological responses occur in the body and mind as preparation for sexual intercourse, and continue during intercourse.  Male arousal  will lead to an  erection , and in  female arousal , the body's response is engorged sexual tissues such as  nipples ,  clitoris ,  vaginal walls , and  vaginal lubrication . [ 1 ]


Mental stimuli  and  physical stimuli  such as touch, and the internal fluctuation of  hormones , can influence sexual arousal. Sexual arousal has several stages and may not lead to any actual sexual activity beyond a mental arousal and the physiological changes that accompany it. Given sufficient sexual stimulation, sexual arousal reaches its climax during an  orgasm . It may also be pursued for its own sake, even in the absence of an orgasm.


Depending on the situation, a person can be sexually aroused by a variety of factors, both physical and mental. A person may be sexually aroused by another person or by particular aspects of that person, or by a non-human object. The physical stimulation of an  erogenous zone  or acts of  foreplay  can result in arousal, especially if it is accompanied with the anticipation of imminent sexual activity. Sexual arousal may be assisted by a  romantic  setting, music or other soothing situation. Sexual arousal can come from  porn  or other sexual material. The potential stimuli for sexual arousal vary from person to person, and from one time to another, as does the level of arousal.


Stimuli can be classified according to the sense involved:  somatosensory  (touch), visual, and  olfactory  (scent).  Auditory stimuli  are also possible, though they are generally considered secondary in role to the other three. [ citation needed ]  Erotic stimuli which can result in sexual arousal can include conversation, reading, films or images, or a smell or setting, any of which can generate erotic thoughts and memories in a person. Given the right context, these may lead to the person desiring physical contact, including  kissing ,  cuddling , and  petting  of an erogenous zone. This may in turn make the person desire direct sexual stimulation of the  breasts ,  nipples ,  buttocks  and/or  genitals , and further  sexual activity .


Erotic stimuli may originate from a source unrelated to the object of subsequent sexual interest. For example, many people may find  nudity ,  erotica  or  pornography  sexually arousing. [ 2 ]  This may generate a general sexual interest that is satisfied by sexual activity. When sexual arousal is achieved by or dependent on the use of objects, it is referred to as  sexual fetishism , or in some instances a  paraphilia .


There is a common belief that women need more time to achieve arousal. However, recent scientific research has shown that there is no considerable difference for the time men and women require to become fully aroused. Scientists from  McGill University Health Centre  in  Montreal  (in Canada) used the method of  thermal imaging  to record baseline  temperature  change in genital area to define the time necessary for sexual arousal. Researchers studied the time required for an individual to reach the peak of sexual arousal while watching sexually explicit movies or pictures and came to the conclusion that on average women and men took almost the same time for sexual arousal — around 10 minutes. [ 3 ]  The time needed for foreplay is strongly individual and varies from one occasion to the next depending on circumstances. [ 3 ]


Unlike many animals,  humans  do not have a  mating season , and both sexes are potentially capable of sexual arousal throughout the year.


Sexual arousal for most people is a positive experience and an aspect of their sexuality, and is often sought. A person can normally control how they will respond to arousal. They will normally know what things or situations are potentially stimulating, and may at their leisure decide to either create or avoid these situations. Similarly, a person's sexual partner will normally also know their partner's erotic stimuli and turn-offs. Some people feel embarrassed by sexual arousal and some are  sexually inhibited . Some people do not feel aroused on every occasion that they are exposed to erotic stimuli, nor act in a sexual way on every arousal. A person can take an active part in a sexual activity without sexual arousal. These situations are considered normal, but depend on the maturity, age, culture and other factors influencing the person.


However, when a person fails to be aroused in a situation that would normally produce arousal and the lack of arousal is persistent, it may be due to a  sexual arousal disorder  or  hypoactive sexual desire disorder . There are many reasons why a person fails to be aroused, including a mental disorder, such as  depression ,  drug use , or a medical or physical condition. The lack of sexual arousal may be due to a general lack of sexual desire or due to a lack of sexual desire for the current partner. A person may always have had no or low sexual desire or the lack of desire may have been acquired during the person's life.


On the other hand, a person may be  hypersexual , which is a desire to engage in sexual activities considered abnormally high in relation to normal development or culture, or suffering from a  persistent genital arousal disorder , which is a spontaneous, persistent, and uncontrollable arousal, and the physiological changes associated with arousal.


Sexual arousal causes various physical responses, most significantly in the  sex organs  (genital organs). Sexual arousal for a man is usually indicated by the  swelling  and  erection  of the  penis  when blood fills the  corpus cavernosum . This is usually the most prominent and reliable sign of sexual arousal in males. In a woman, sexual arousal leads to increased blood flow to the  clitoris  and the rest of the  vulva , as well as vaginal transudation - the seeping of moisture through the vaginal walls, which serves as  lubrication . In both sexes, pupil dilation is an involuntary physiological response to sexual arousal. [ 4 ]  However, the degree of pupil dilation varies with individuals, as does the degree of maximal pupil dilation. [ 5 ] [ 6 ]


In males:


It is normal to correlate the  erection  of the  penis  with male sexual arousal. Physical or psychological stimulation, or both, leads to  vasodilation  and the increased blood flow engorges the three spongy areas that run along the length of the penis (the two  corpora cavernosa  and the  corpus spongiosum ). The penis grows enlarged and firm, the skin of the  scrotum  is pulled tighter, and the  testicles  are pulled up against the body. [ 7 ]  However, the relationship between erection and arousal is not one-to-one (arousal non-concordance). [ 8 ]  After their mid-forties, some men report that they do not always have an erection when they are sexually aroused. [ 9 ]  Equally, a male erection can occur during sleep ( nocturnal penile tumescence ) without conscious sexual arousal or due to mechanical stimulation (e.g., rubbing against the bed sheet) alone. A young man—or one with a strong libido—may experience enough sexual arousal for an erection to result from a passing thought, or just the sight of a passerby. Once erect, his penis may gain enough stimulation from contact with the inside of his clothing to maintain and encourage it for some time. [ 10 ]


As sexual arousal and stimulation continues, it is likely that the  glans  or head of the erect penis will swell wider and, as the genitals become further engorged with blood, their color deepens and the testicles can grow up to 50% larger. As the testicles continue to rise, a feeling of warmth may develop around them and the  perineum . With further sexual stimulation, their heart rate increases, blood pressure rises and breathing becomes quicker. [ 7 ]  The increase in blood flow in the genital and other regions may lead to a  sex flush  in some men. [ 11 ]


As sexual stimulation continues,  orgasm  begins, when the muscles of the  pelvic floor , the  vasa deferentia  (between the testicles and the prostate), the  seminal vesicles  and the  prostate  gland itself may begin to contract in a way that forces sperm and semen into the  urethra  inside the penis. Once this has started, it is likely that the man will continue to  ejaculate  and orgasm fully, with or without further stimulation.


Equally, if sexual stimulation stops before orgasm, the physical effects of the stimulation, including the  vasocongestion , will subside in a short time. Repeated or prolonged stimulation without orgasm and ejaculation can lead to discomfort in the testes (corresponding to the slang term " blue balls " [ 12 ] ).


After ejaculation, men usually experience a  refractory period  characterized by loss of their erection, a subsidence in any sex flush, less interest in sexual activity, and a feeling of relaxation that can be attributed to the  neurohormones   oxytocin  and  prolactin . [ 13 ]  The intensity and duration of the refractory period can be very short in a highly aroused young man in a highly arousing situation, perhaps without even a noticeable loss of erection. It can be as long as a few hours or days in middle-aged and older men. [ 7 ]


The beginnings of sexual arousal in a woman's body is usually marked by  vaginal lubrication  (wetness; though this can occur without arousal due to infection or cervical mucus production around ovulation), swelling and engorgement of the  vulva , and internal lengthening and enlargement of the  vagina . [ 14 ]  There have been studies to find the degree of correlation between these physiological responses and the woman's subjective sensation of being sexually aroused: the findings usually are that in some cases there is a high correlation, while in others, it is surprisingly low. [ 15 ]


Further stimulation can lead to additional vaginal wetness and further engorgement and swelling of the  clitoris  and the  labia , along with increased redness or darkening of the skin in these areas as blood flow increases. Further changes to the internal organs also occur including to the internal shape of the vagina and to the position of the  uterus  within the  pelvis . [ 14 ]  Other changes include an increase in  heart rate  as well as in  blood pressure , feeling hot and flushed and perhaps experiencing tremors. [ 16 ]  A  sex flush  may extend over the chest and upper body.


If sexual stimulation continues, then sexual arousal may peak into  orgasm . After orgasm, some women do not want any further stimulation and the sexual arousal quickly dissipates. Suggestions have been published for continuing the sexual excitement and moving from one orgasm into further stimulation and maintaining or regaining a state of sexual arousal that can lead to second and subsequent orgasms. [ 17 ]  Some women have experienced such multiple orgasms quite spontaneously.


While young women may become sexually aroused quite easily, and reach orgasm relatively quickly with the right stimulation in the right circumstances, there are physical and psychological changes to women's sexual arousal and responses as they age. Older women produce less vaginal lubrication and studies have investigated changes to degrees of satisfaction, frequency of sexual activity, to desire, sexual thoughts and  fantasies , sexual arousal, beliefs about and attitudes to sex, pain, and the ability to reach orgasm in women in their 40s and after  menopause . Other factors have also been studied including socio-demographic variables, health, psychological variables, partner variables such as their partner's health or sexual problems, and lifestyle variables. It appears that these other factors often have a greater impact on women's sexual functioning than their menopausal status. It is therefore seen as important always to understand the "context of women's lives" when studying their sexuality. [ 18 ]


Reduced  estrogen  levels may be associated with increased vaginal dryness and less  clitoral erection  when aroused, but are not directly related to other aspects of sexual interest or arousal. In older women, decreased pelvic muscle tone may mean that it takes longer for arousal to lead to orgasm, may diminish the intensity of orgasms, and then cause more rapid resolution. The uterus typically contracts during orgasm and, with advancing age, those contractions may actually become painful. [ 18 ]


Psychological sexual arousal involves appraisal and evaluation of a stimulus, categorization of a stimulus as sexual, and an affective response. [ 19 ]  The combination of cognitive and physiological states elicits psychological sexual arousal. [ 19 ] [ 20 ]  Some suggest that psychological sexual arousal results from an interaction of cognitive and experiential factors, such as affective state, previous experience, and current social context. [ 21 ]


The relationship between  sexual desire  and arousal in men is complex, with a wide range of factors increasing or decreasing sexual arousal. [ 22 ]  Physiological responses, such as  heart rate ,  blood pressure , and  erection , are often discordant with self-reported subjective perceptions of arousal. [ 23 ]  This inconsistency suggests that psychological or cognitive aspects also have a strong effect on sexual arousal. The cognitive aspects of sexual arousal in men are not completely known, but the state does involve the appraisal and evaluation of the stimulus, categorization of the stimulus as sexual, and an affective response. [ 24 ]  Research suggests that cognitive factors, such as sexual motivation, perceived  gender role  expectations, and sexual attitudes, contribute to sex differences observed in subjective sexual arousal. Specifically, while watching heterosexual  erotic videos , men are more influenced by the sex of the actors portrayed in the stimulus, and men may be more likely than women to objectify the actors. [ 25 ] [ 26 ]  There are reported differences in brain activation to sexual stimuli, with men showing higher levels of  amygdala  and  hypothalamic  responses than women. This suggests the amygdala plays a critical role in the processing of sexually arousing visual stimuli in men. [ 27 ]


Research suggests that cognitive factors like sexual motivation, perceived  gender role  expectations, and sexual attitudes play important roles in women's self-reported levels of sexual arousal. [ 21 ]  In her alternative model of sexual response, Basson [ 28 ] [ 29 ]  suggests that women's need for  intimacy  prompts them to engage with sexual stimuli, which leads to an experience of  sexual desire  and psychological sexual arousal. Psychological sexual arousal also has an effect on physiological mechanisms; Goldey and van Anders [ 30 ]  showed that sexual cognitions impact hormone levels in women, such that sexual thoughts result in a rapid increase in  testosterone  in women who were not using  hormonal contraception . In terms of brain activation, researchers have suggested that  amygdala  responses are not solely determined by level of self-reported sexual arousal; Hamann and colleagues [ 27 ]  found that women self-reported higher sexual arousal than men, but experienced lower levels of amygdala responses.


During the late 1950s and early 1960s,  William H. Masters and Virginia E. Johnson  conducted multiple studies into  human sexuality . In 1966, they published  Human Sexual Response , detailing four stages of physiological changes in humans during sexual stimulation: excitement, plateau, orgasm, and resolution. [ 31 ]


Barry Singer presented a model of the process of sexual arousal in 1984, in which he conceptualized human sexual response to be composed of  three independent but generally sequential components . The first stage,  aesthetic response,  is an emotional reaction to noticing an attractive face or figure. This emotional reaction produces an increase in attention toward the object of attraction, typically involving head and eye movements toward the attractive object. The second stage,  approach response,  progresses from the first and involves bodily movements towards the object. The final  genital response  stage recognizes that with both attention and closer proximity, physical reactions result in genital tumescence. Singer also stated that there is an array of other autonomic responses, but acknowledges that the research literature suggests that the genital response is  the most reliable and convenient to measure  in males. [ 32 ]


In 2000, Rosemary Basson presented an alternative model to the human sexual response cycle that is  specific to women's sexual response . [ 33 ]  She argues that gender differences in  sex drive , sexual motivation, sexual concordance, and capacity for orgasm underlie the need for an alternative model of sexual response. While the human sexual response cycle begins with desire, followed by arousal, orgasm, and finally resolution, Basson's [ 29 ]  alternative model is circular and begins with women feeling a need for  intimacy , which leads her to seek out and be receptive to sexual stimuli; women then feel sexual arousal, in addition to  sexual desire . The cycle results in an enhanced feeling of intimacy. Basson emphasizes the idea that a lack of spontaneous desire should not be taken as an indication of  female sexual dysfunction ; many women experience sexual arousal and responsive desire simultaneously when they are engaged in sexual activity. [ 33 ]


Frederick Toates presented a model of sexual motivation, arousal, and behavior in 2009 that combines the principles of  incentive-motivation theory  and  hierarchical control of behavior . The  basic incentive-motivation model  of sex suggests that incentive cues in the environment invade the nervous system, which results in sexual motivation. Positive sexual experiences enhance motivation, while negative experiences reduce it. Motivation and behaviour are organized  hierarchically ; each are controlled by a combination of direct (external stimuli) and indirect (internal cognitions) factors. Excitation and inhibition of behavior act at various levels of this hierarchical structure. For instance, an external stimulus may directly excite sexual arousal and motivation below a conscious level of awareness, while an internal cognition can elicit the same effects indirectly, through the conscious representation of a sexual image. In the case of inhibition, sexual behavior can be active or conscious (e.g., choosing not to have sex) or it can be passive or unconscious (e.g., being unable to have sex due to fear). Toates emphasizes the importance considering  cognitive  representations in addition to external stimuli; he suggests that mental representations of incentives are interchangeable with excitatory external stimuli for eliciting sexual arousal and motivation. [ 34 ]


This model created by  John Bancroft  and Erick Janssen, previously at the Kinsey Institute, explores the  individual variability of sexual response .  They postulate that this variability depends on the interaction between an individual's sexual excitation system (SES) and sexual inhibition system (SIS). Popularized by  Emily Nagoski 's self-help book  Come as You Are , the SES has been described as the sexual response's 'accelerator' and the SIS as the 'brake'. [ 35 ]   The SIS/SES questionnaire was developed to assess an individual's SIS and SES levels.  A  factor analysis  of the SIS/SES questionnaire, revealed a single excitation factor and two inhibition factors.  These inhibition factors were interpreted as SIS1 (inhibition due to the threat of performance failure) and SIS2 (inhibition due to the threat of performance consequences).


The SIS/SES questionnaire was originally developed for men though it has since proven its statistical validity among women. Despite this, the SESII-W (the Sexual Excitation/Sexual Inhibition Inventory for Women) was created by Graham and associates. [ 36 ]  Female focus groups found that the context of the emotional relationship between sexual partners was not fully represented in the original SIS/SES questionnaire.  A factor analysis of this questionnaire revealed only two factors: sexual excitation (SE) and sexual inhibition (SI).  This may point to internal inconsistencies in the SIS/SES questionnaire regarding gender.  One lower order factor in the SESII-W labeled Arousal Contingency was particularly relevant; this factor explains the easy disruption of sexual arousal.


Regardless of the difference in these two questionnaires, both surveys' scores show normal distribution verifying the hypothesis that there is a normal individual variation in sexual arousal and inhibition.  In the original SIS/SES questionnaire, statistically significant gender differences are seen despite considerable overlap in scores between men and women.  On average, males score higher on sexual excitation and lower than females on both facets of sexual inhibition. The differences in scores between genders have not been explained beyond the theoretical level.


The source of individual variability on the sexual excitation and inhibition systems is not known definitively.  Even less is known about how these systems develop in individuals.  Age of first  masturbation  has been used as a measure to assess sexual development. Age of masturbatory onset is much more variable in girls than boys, whose tend to be close to puberty. [ 37 ]  Researchers have not determined whether this gender difference is biological in nature or influenced by sociocultural values.  One twin-study has found evidence for the heritability of both factors of SIS, but research suggests that SES variability is down to environmental factors. [ 38 ]


The majority of studies investigating sexual functioning use heterosexual participants exclusively, limiting the generalizability of the dual control model. One study comparing heterosexual and  gay men  found that gay men had similar scores for SIS2, but scored significantly higher for SIS1 and SES. [ 39 ]  Heterosexual, lesbian, and bisexual women's scores on the SESII-W found that bisexual women scored higher on SES than the other groups and heterosexual women scored higher on the sexual inhibition factor than both the lesbian and bisexual women. [ 40 ]  More studies need to be done using the dual control model to gain a more broad view of sexual orientation and sexual arousability.


One way to study sexual arousal in women and men is to conduct sexual psychophysiological research in a laboratory setting. This field of research looks at physical sexual responses in addition to mental and emotional experiences of sexual arousal. [ 41 ]


Various hypotheses and theories have been propounded in order to establish the biological bases for sexual arousal in humans.  Ivan Tarkhanov  showed, in experiments on cutting and artificial emptying of the  seminal vesicles , that the latter played the crucial role in the generation of sexual excitement in frogs. Proceeding from these experimental results, Tarkhanov put forward a hypothesis that filling and evacuation of the seminal vesicles were the main biological cause, which led to sexual arousal and its disappearance in humans and other mammals. [ 42 ]  Ever since Tarkhanov's findings demonstrated sexual arousal in frogs to result from the state of seminal vesicles, the attempted elucidation of their role in other animals' sexual behaviour has been the object of experimental effort. No generalisation has yet appeared, however. The study performed by Beach & Wilson ( University of California, Berkeley ) in 1964 discovered that these glands do not participate in the regulation of sexual arousal of male rats in the similar manner. [ 43 ]  Whether the regularity observed in frogs is applicable to humans remains unknown. Unambiguous experimental evidence for the existence of the Tarkhanov regularity in human sexual behaviour has never been obtained. [ 44 ] [ 45 ]


Another explanation of sexual arousal is offered by the approach, which  Kazimierz Imieliński  calls the "psychohydraulic model of sexuality". This point of view likens human sexuality to a steam boiler, with biological processes or internal irritants creating sexual tension. If the level of this tension reaches threshold, sexual arousal occurs as the expression of necessity to let off steam. Gary F. Kelly ( Clarkson University ) describes this model as follows:


For centuries, the assumption was made that the longing for  sexual interaction  was innate, and an inner drive model was used to explain it. It has been suggested that this model was much like a metaphor for a steam boiler. Internal sexual "steam" would build up until the pressure became so great that the drive to release it was very strong. This view also assumed that there was some adverse physical consequence of not releasing the pressure. [ 46 ] : 95


The "psychohydraulic model of sexuality" has been formulated most definitely in  psychoanalysis :


The instinct causes tensions within the central nervous system, which spread out over the whole being; it is urgent and irresistible in nature and constantly repeats itself. ... An erection, for example, is pleasurable and painful at the same time. With an increase of sexual excitation, the tension increases and becomes wholly unpleasurable. This condition becomes so unbearable that the individual is forced to seek release from these tensions and liberation from the painful feelings. ... The pain of tension which accompanies the increase in the intensity of the instinctual drives changes, with the discharge, into the pleasure of relaxation. [ 47 ] : 55, 56


After a certain time, the same process begins anew. Such an approach assumes sexual arousal to be a spontaneous desire that appears periodically like sensations of hunger and thirst. Drawing a parallel between these sensations and sexual excitation is widely accepted now: "Everyone must experience sexuality in some way to survive. ... In this sense sex is a necessity of life, just as air, food, and warmth." [ 48 ] : 190   And yet there is no empirical evidence in support of such a parallel, Imieliński says. Sensations of hunger and thirst occur due to certain states of physiological insufficiency. The feeling of hunger results from the lack of glucose, fats and amino acids in blood. The feeling of thirst occurs in response to reduction of the water content of tissues. None of similar states of physiological deficiency responsible for the periodical appearance of sexual arousal has been revealed in human sexuality. [ 49 ]


Sexual arousal in women is characterized by  vasocongestion  of the  genital  tissues, including internal and external areas (e.g.,  vaginal walls ,  clitoris , and  labia ). There are a variety of methods used to assess genital sexual arousal in women.  Vaginal photoplethysmography  (VPG) can measure changes in vaginal blood volume or phasic changes in vasocongestion associated with each heartbeat.  Clitoral photoplethysmography  functions in a similar way to VPG, but measures changes in clitoral blood volume, rather than vaginal vasocongestion.  Thermography  provides a direct measure of genital sexual arousal by measuring changes in  temperature  associated with increased blood flow to the  vulvar  tissues. Similarly,  labial thermistor clips  measure changes in temperature associated with genital engorgement; this method directly measures changes in temperature of the labia. More recently,  laser doppler imaging  (LDI) has been used as a direct measure of genital sexual arousal in women. LDI functions by measuring superficial changes in blood flow in the vulvar tissues.


The most obvious response involved with sexual behaviour in males is  penile erection . The use of the volume (or circumference) change during penile erection as a convenient measure of sexual arousal was first developed by  Kurt Freund . [ 50 ]  This measurement of blood flow to the male genitals is known as penile plethysmography. This is commonly measured using a strain gauge, a simple mercury strain gauge encompassed in a ring of rubber. The ring surrounds the  penis , but does not constrict or cause discomfort. [ 51 ]  The measure has been found by some to be a reliable and valid measurement of male arousal. [ 52 ]  More recently,  thermography  has been developed to measure the physiological measurements of sexual arousal. Studies have found temperature change specific to the genitals during sexual arousal, which supports the validity of this measure. [ 53 ]


Category-specificity refers to a person showing sexual arousal to the categories of people they prefer to have sex with. Sexual arousal studies involving category-specificity look at genital responses (physiological changes), as well as subjective responses (what people report their arousal levels to be). Category-specific sexual arousal is more commonly found amongst men than women. [ 54 ] [ 55 ]   Heterosexual  men experience much higher genital and subjective arousal to women than to men. This pattern is reversed for  homosexual  men. [ 56 ]


Studies have found that women have a non-category-specific genital response pattern of sexual arousal, meaning their genital responses are only modestly related to their preferred category. [ 57 ]  On the other hand, female subjective responses are category-specific, because they typically report their highest level of arousal to their preferred stimulus, although the reported difference in levels of arousal is typically much smaller than those in men. [ 58 ]  A possible explanation for the non-category specific genital arousal in women, which also accounts for their high individual variation, is the "preparation hypothesis". This hypothesis suggests that, provided there is enough of an increase in vaginal blood flow for  vaginal lubrication  to occur in a sexual context, the magnitude of arousal need not be consistent. That is, the hypothesis is that vaginal lubrication can take place as a protective mechanism even in a non-preferred sexual situation, such as when sexual activity is  non-consensual . [ 58 ]


Other researchers argue that since the research is done on people who volunteer to be studied, the observed levels of category specificity may not represent the population, that there may be different cultural expectations of sexual interests being linked to genital arousal that make men with non-category specific genital arousal less likely to appear as test subjects. There researchers also argue that the assumption that men are always sexually interested in what causes genital arousal removes its own falsifiability by explaining all contradictory data away as "denial", making the theory untestable. [ 59 ] [ 60 ]


While there is disagreement among neurologists on whether or not it is possible to categorically distinguish male brains and female brains by measuring many variables in the brain, neurologists agree that all single variables in the brain display more individual variation and overlap between the sexes than differences between the sexes. For instance, men and women alike are capable of classifying sex acts as sexual no matter if they find them appealing or not, making a genital response to unappealing erotic stimuli a single mechanism step. It is therefore argued by neurologists that category specificity of genital response to erotical imagery, being determined by one or a small number of closely linked brain mechanisms and therefore not subject to significant multivariate effects, cannot be subject to such a large sex difference as that apparent in pletysmographic studies. These neurologists cite the existence of significant volunteering bias among men but not women in erotica research, in particular that the overrepresentation of erectile dysfunction yet underrepresentation of sexuality-related shame in volunteers is consistent with the hypothesis that genital response to both sexual relevance and appeal allows for a stronger erectile function than response only to appeal and that a majority of the male population are ashamed of their responses to unappealing stimuli, accounting for the discrepancy between the report from most heterosexual couples that male erection is faster than female lubrication and the appearance on pletysmography volunteers that female lubrication is at least as fast as male erection. They also argue that the appearance of a greater individual variability in female genital response than in male genital response is consistent with a representative female sample and a male sample subject to bias that leaves much of the individual variability unstudied, with a reference to the neurological observation that all brain structures display significant individual variability in both sexes and that no brain structure is variable only in females and not in males. [ 61 ] [ 62 ]


Sexual arousal results in a combination of physiological and psychological factors, like genital sexual response and subjective experience of sexual arousal. The degree to which genital and subjective sexual response correspond is termed  concordance .
Arousal non-concordance is when there is no link, for example, in morning erection, which happens both with men ( nocturnal penile tumescence ) and women ( nocturnal clitoral tumescence ), or in cases of  rape  where research confirms reports of an arousal non-concordance orgasm or orgasm alike event can take place – presumably as a measure to protect the internal organs of the vagina. [ 63 ]


Research has shown a  reliable  gender difference in concordance of sexual arousal, such that men have a higher level of concordance between genital and subjective sexual responding than women do. [ 64 ]  Some researchers argue that this gender difference can be attributed to the type of method used to assess genital responding in women. There may be a difference in women's ability to perceive  internal  versus  external genital  engorgement subjectively, as measured by vaginal photoplethysmography (VPG) and  thermography  respectively. Chivers and colleagues [ 65 ]  found that men's and women's concordance was more similar when thermography was used as a measure of genital sexual arousal than when VPG was used. However, few studies using thermography have been conducted and further research is required to determine whether the gender difference in concordance is a measurement artifact or a true phenomenon.


Several  hormones  affect sexual arousal, including  testosterone ,  cortisol , and  estradiol . However, the specific roles of these hormones are not clear. [ 66 ]  Testosterone is the most commonly studied hormone involved with sexuality. It plays a key role in sexual arousal in males, with strong effects on central arousal mechanisms. [ 66 ]   The connection between testosterone and sexual arousal is more complex in females. Research has found testosterone levels increase as a result of sexual cognitions in females that do not use  hormonal contraception . [ 67 ]  Also, women who participate in  polyandrous  relationships have higher levels of testosterone. However, it is unclear whether higher levels of testosterone cause increased arousal and in turn multiple partners or whether sexual activity with multiple partners cause the increase in testosterone. [ 68 ]  Inconsistent study results point to the idea that while testosterone may play a role in the sexuality of some women, its effects can be obscured by the co-existence of psychological or affective factors in others. [ 66 ]


While human sexuality is well understood, scientists do not completely grasp how other animals relate sexually. However, current research studies suggest that many animals, like humans, enjoy sexual relations that are not limited to reproduction.  Dolphins  and  bonobos , for example, are both well known to use sex as a "social tool to strengthen and maintain bonds". [ 69 ]   Ethologists  have long documented the exchanges of sex to promote group cohesion in  social animals . Cementing social bondage is one of the most prominent theorized selective advantages of  group selection  theory. Experts in the  evolution of sex  such as  John Maynard Smith  advocate for the idea that the exchange of sexual favors helps congeal and localize the assortment of  alleles  in isolated population and therefore is potentially a very strong force in  evolution . Smith has also written extensively on the "seminal fluid swapping theory" logistic application of the assortment of alleles as a more accurate synthetic depiction of the  Hardy–Weinberg principle  in cases of severely interbreeding populations.


The effect of sexual response is thought to be a plastic positive reinforcement behavior modifier associated with the  Baldwin effect . The display of  secondary sex characteristics  in humans such as a penis-like enlarged  clitoris  in females during arousal and  gynecomastia  in males are thought to have once been objects of  mate selection  in human evolution because of the persistence of the phenomenon of these features invoking sexual arousal for potential mates in  cross-cultural studies . [ 70 ]  A dramatic example of this is the high rates of secondary sex characteristic  dimorphism  in some Southeast Asia human populations. [ 71 ]  Similar evolutionary stimuli may also have resulted in novel structures such as the  pseudo-penis  of the female  spotted hyena . [ 72 ]


An  erection  (clinically:  penile erection  or  penile tumescence ) is a  physiological  phenomenon in which the  penis  becomes firm, engorged, and enlarged. Penile erection is the result of a complex interaction of psychological, neural, vascular, and endocrine factors, and is often associated with  sexual arousal ,  sexual attraction  or  libido , although erections can also be spontaneous. The shape, angle, and direction of an erection vary considerably between humans.


Physiologically, an erection is required for a male to effect penetration or  sexual intercourse  and is triggered by the  parasympathetic  division of the  autonomic nervous system , causing the levels of  nitric oxide  (a  vasodilator ) to rise in the  trabecular   arteries  and  smooth muscle  of the penis. The arteries  dilate  causing the  corpora cavernosa  of the penis (and to a lesser extent the  corpus spongiosum ) to fill with  blood ; simultaneously the  ischiocavernosus  and  bulbospongiosus  muscles compress the  veins  of the corpora cavernosa restricting the egress and circulation of this blood. Erection subsides when parasympathetic activity reduces to baseline.


As an autonomic nervous system response, an erection may result from a variety of stimuli, including  sexual stimulation  and  sexual arousal , and is therefore not entirely under conscious control. Erections during sleep or upon waking up are known as  nocturnal penile tumescence  (NPT), also known as "morning wood". Absence of nocturnal erection is commonly used to distinguish between physical and psychological causes of  erectile dysfunction  and  impotence .


The state of a penis which is partly, but not fully, erect is sometimes known as semi-erection (clinically:  partial tumescence ); a penis which is not erect is typically referred to as being flaccid, or soft.


An erection is necessary for  natural insemination  as well as for the harvesting of sperm for  artificial insemination , and is common for children and infants. After reaching  puberty , erections occur much more frequently. [ 1 ] [ 2 ]
An erection occurs when two tubular structures, called the  corpora cavernosa , that run the length of the penis, become engorged with  venous blood . This may result from any of various  physiological  stimuli, also known as  sexual stimulation  and  sexual arousal . The  corpus spongiosum  is a single tubular structure located just below the corpora cavernosa, which contains the  urethra , through which  urine  and  semen  pass during  urination  and  ejaculation  respectively. This may also become slightly engorged with blood, but less so than the corpora cavernosa.


In some cases, the scrotum becomes tightened during an erection, and in most uncircumcised males, the  foreskin  automatically and gradually retracts throughout the various stages of erection, exposing the  glans , though some individuals have to manually retract their foreskin.


In the presence of mechanical stimulation, erection is initiated by the  parasympathetic  division of the  autonomic nervous system  with minimal input from the  central nervous system . Parasympathetic branches extend from the  sacral plexus  into the  arteries  supplying the erectile tissue; upon stimulation, these nerve branches release  acetylcholine , which in turn causes the release of  nitric oxide  from  endothelial cells  in the  trabecular  arteries. [ 3 ]  Nitric oxide diffuses to the  smooth muscle  of the arteries (called  trabecular smooth muscle [ 4 ] ), acting as a  vasodilating  agent. [ 5 ]   The arteries dilate, filling the  corpus spongiosum  and  corpora cavernosa  with blood.  The  ischiocavernosus  and  bulbospongiosus  muscles also compress the veins of the corpora cavernosa, limiting the venous drainage of blood. [ 6 ]  Erection subsides when parasympathetic stimulation is discontinued; baseline stimulation from the  sympathetic division  of the autonomic nervous system causes constriction of the  penile arteries  and cavernosal sinosoids, forcing blood out of the erectile tissue through erection-related veins which include one deep dorsal vein, a pair of cavernosal veins, and two pairs of para-arterial veins between Buck's fascia and the tunica albuginea. [ 7 ] [ 8 ]  Erection rigidity is mechanically controlled by reduction blood flow through theses veins, and thereby building up the pressure of the corpus cavernosum and corpus spongiosum, an integral instructure, the distal ligament, buttresses the glans penis. [ 9 ]


After  ejaculation  or cessation of stimulation, erection usually subsides, but the time taken may vary depending on the length and thickness of the penis. [ 10 ]


The  cerebral cortex  can initiate erection in the absence of direct mechanical stimulation (in response to visual, auditory, olfactory, imagined, or tactile stimuli) acting through erectile centers in the lumbar and sacral regions of the  spinal cord . [ 11 ]  The cortex may suppress erection, even in the presence of mechanical stimulation, as may other psychological, emotional, and environmental factors. [ 12 ]


The penis may become erect during sleep or be erect on waking up. Such an erection is medically known as  nocturnal penile tumescence  (informally:  morning wood  or  morning glory ). [ 13 ] [ 14 ] [ 15 ] [ 16 ]


Though an erection can have many causes, it is most commonly seen as an indicator of  sexual arousal  and is therefore considered taboo or inappropriate for a public setting in many societies. This taboo is lesser than that surrounding  public sex  but higher than that surrounding  nudity . Erectile dysfunction is often considered a flaw, eliciting shame in individuals affected.


The  penile plethysmograph , which measures erections, has been used by some governments and  courts of law  to measure sexual orientation. An unusual aversion to the erect penis is sometimes referred to as  phallophobia .


Spontaneous erections, also known as involuntary, random or unwanted erections, are commonplace and a normal part of male physiology. Socially, such erections can be  embarrassing  if they happen in public or when undesired. [ 1 ]  Such erections can occur at any time of day, and if clothed may cause a bulge which (if required) can be disguised or hidden by wearing close-fitting underwear, a long shirt, or baggier clothes. [ 17 ]


The length of the flaccid penis is not indicative of the length of the penis when it becomes erect, with some smaller flaccid penises growing much longer, and some larger flaccid penises growing comparatively less. [ 18 ]
Generally, the size of an erect penis is fixed throughout post- pubescent  life. Its size may be increased by surgery. [ 19 ]


Though the size of a penis varies considerably between males, the average length of an erect  human penis  is 13.12 cm (5.17 inches), while the average circumference of an erect human penis is 11.66 cm (4.59 inches). [ 20 ]


Although many erect penises point upwards, it is common and normal for the erect penis to point nearly vertically upwards or horizontally straight forward or even nearly vertically downwards, all depending on the tension of the suspensory ligament that holds it in position. An erect penis can also take on a number of different shapes, ranging from a straight tube to a tube with a curvature up or down or to the left or right. An increase in penile curvature can be caused by  Peyronie's disease . This may cause physical and psychological effects for the affected individual, which could include  erectile dysfunction  or pain during an erection. Treatments include oral medication (such as  colchicine ) or surgery, which is most often performed only as a last resort.
The following table shows how common various erection angles are for a standing male. In the table, zero degrees (0°) is pointing straight up against the abdomen, 90° is horizontal and pointing straight forward, and 180° is pointing straight down to the feet. An upward pointing angle is most common and the average erection angle is 74.3 degrees. The penile curvature was measured same time. 63% men have straight penis. 22.2% men have upwards curvature and 14.8% men have downwards curvature. [ 21 ]


Erectile dysfunction (also known as ED or "(male) impotence") is a  sexual dysfunction  characterized by the inability to develop and/or maintain an erection. [ 22 ] [ 23 ]  The study of erectile dysfunction within medicine is known as  andrology , a sub-field within  urology . [ 24 ]


Erectile dysfunction may occur due to  physiological  or  psychological  reasons, most of which are amenable to treatment. Common physiological reasons include diabetes, kidney disease, chronic alcoholism, multiple sclerosis, atherosclerosis, vascular disease, including arterial insufficiency and venogenic erectile dysfunction, [ 25 ]  and neurologic disease which collectively account for about 70% of ED cases. [ 5 ]  Some drugs used to treat other conditions, such as  lithium  and  paroxetine , may cause erectile dysfunction. [ 23 ] [ 26 ]


Erectile dysfunction, tied closely as it is to cultural notions of  potency ,  success  and  masculinity , can have devastating psychological consequences including feelings of  shame ,  loss  or inadequacy. [ 27 ]  There is a strong  culture of silence  and inability to discuss the matter. Around one in ten men experience recurring impotence problems at some point in their lives. [ 28 ]


Priapism  is a painful condition in which the penis does not return to its flaccid state, despite the absence of both physical and psychological stimulation. Priapism lasting over four hours is a medical emergency.


Hard flaccid syndrome  is a rare, chronic condition characterized by a flaccid penis that remains in a firm, semi-rigid or semi-erect state in the absence of sexual arousal.


At the time of penetration, the  canine penis  is not erect, and only able to penetrate the female because it includes a narrow bone called the  baculum , a feature of most  placental mammals . After the male achieves penetration, he will often hold the female tighter and thrust faster, and it is during this time that the male's penis expands, unlike human sexual intercourse, where the male penis commonly becomes erect before entering the female. [ 29 ]


An elephant's penis is S-shaped when fully erect and has a Y-shaped  orifice . [ 30 ]


Given the small amount of erectile tissue in a  bull's penis , there is little enlargement after erection. The penis is quite rigid when non-erect, and becomes even more rigid during erection. Protrusion is not affected much by erection, but more by relaxation of the  retractor penis muscle  and straightening of the sigmoid flexure. [ 31 ] [ 32 ]


A male  fossa 's penis reaches to between his forelegs when erect. [ 33 ]


When not erect, a  horse's penis  is housed within the prepuce, 50 centimetres (20 in) long and 2.5 to 6 centimetres (0.98 to 2.36 in) in diameter with the distal end 15 to 20 centimetres (5.9 to 7.9 in). The  retractor muscle  contracts to retract the penis into the sheath and relaxes to allow the penis to extend from the sheath. [ 34 ]  When erect, the penis doubles in length [ 35 ]  and thickness and the  glans  increases by 3 to  4 times . [ 34 ]  Erection and protrusion take place gradually, by the increasing  tumescence  of the erectile vascular tissue in the  corpus cavernosum penis . [ 36 ] [ 37 ]  Most stallions achieve erection within 2 minutes of contact with an estrus mare, and mount the estrus mare 5–10 seconds afterward. [ 38 ]


A  bird penis  is different in structure from  mammal penises , being an erectile expansion of the cloacal wall and being erected by  lymph , not blood. [ 39 ]   The penis of the  lake duck  can reach about the same length as the animal himself when fully erect, but more commonly is about half the bird's length. [ 40 ] [ 41 ]


Clinically, erection is often known as "penile erection", and the state of being erect, and process of erection, are described as "tumescence" or "penile tumescence". The term for the subsiding or cessation of an erection is " detumescence ".


Colloquially  and in  slang , erection is known by many informal terms. Commonly encountered  English  terms include 'stiffy', 'hard-on', 'boner' and 'woody'. [ 42 ]  There are several slang words, euphemisms and synonyms for an erection in English and in other languages (see also:  The WikiSaurus entry ).


An  erogenous zone  (from Greek  ἔρως ,  érōs  "love"; and English  -genous  "producing", from Greek  -γενής ,  -genḗs  "born") is an area of the  human body  that has heightened  sensitivity , the  stimulation  of which may generate a sexual response such as relaxation,  sexual fantasies ,  sexual arousal , and  orgasm .


Erogenous zones are located all over the human body, but the sensitivity of each varies, and depends on concentrations of nerve endings that can provide pleasurable sensations when stimulated. The touching of another person's erogenous zone is regarded as an act of  physical intimacy . Whether a person finds stimulation in these areas to be pleasurable or objectionable depends on a range of factors, including their level of arousal, the circumstances in which it takes place, the cultural context, the nature of the relationship between the partners, and the partners' personal histories.


Erogenous zones may be classified by the type of sexual response that they generate. Many people are gently aroused when their eyelids, eyebrows, temples, shoulders, hands, arms, and hair are subtly touched. Gently touching or stroking of these zones stimulates a partner during  foreplay  and increases the arousal level. Also, the gentle massage or stroke of the abdominal area along with kissing or simply touching the navel can be a type of stimulation.


Specific zones are associated with sexual response, and include the lips and nipples in addition to areas of the genitals, notably  corona  of the  glans penis ,  clitoris  and  perianal skin . [ citation needed ]  These zones have a high density of innervation, and may have an efficiency of wound healing and a capacity to stimulate generalized cerebral arousal. [ 1 ]


In these zones, the skin is similar to normal-haired skin and has the normal high density of nerves and hair follicles. These areas include the sides and back of the  neck , the inner arms, the  axillae  (armpits) and sides of the  thorax  (chest). [ citation needed ]


For males, erogenous zones consist of the  glans  and the  penis  itself, along with the  scrotum , the  perineum , and the  anus . [ 2 ]


Males may also experience sexual stimulation via the  prostate , either from  anal sex  or  massage .


For females, parts of the  vulva , especially the  clitoris , as well as the  perineum  and  anus , are erogenous zones. [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ]


While the  vagina  is not especially sensitive as a whole, its lower third (the area close to the entrance) has concentrations of the nerve endings that can provide pleasurable sensations during sexual activity when stimulated; this is also called the anterior wall of the vagina or the outer one-third of the vagina, and it contains the majority of the vaginal nerve endings, making it more sensitive to touch than the inner two-thirds of the vaginal barrel. [ 4 ] [ 5 ] [ 8 ] [ 9 ]


Within the anterior wall of the vagina, there is a patch of ribbed rough tissue which has a texture that is sometimes described as similar to the palate (the roof of a mouth) or a raspberry, and may feel spongy when a woman is sexually aroused. This is the  urethral sponge , which may also be the location of an area that some women report is an erogenous zone; this is sometimes called the  G-spot . When stimulated, it may lead to sexual arousal, an orgasm, or  female ejaculation . [ 10 ]  The existence of the G-spot and whether or not it is a distinct structure is debated among researchers, as reports of its location vary from woman to woman, it appears to be nonexistent in some women, and scientists commonly believe that it is an extension of the clitoris. [ 5 ] [ 11 ] [ 12 ] [ 13 ]


The lips and tongue are sensitive and can be stimulated by  kissing  and licking. Biting at the lip can also provide stimulus.


The neck, clavicle area and the back of the neck are very sensitive, and can be stimulated by licking, kissing or light caressing. Some people also like being bitten gently in these areas, often to the point that a " hickey ", or "love-bite" is formed. [ 5 ]


Some people find whispering or breathing softly in the ear to be pleasurable and relaxing, as well as licking, biting, caressing and/or kissing it especially the area of and behind the  earlobe .


The  areola  and  nipple  contain  Golgi-Mazzoni , Vater-Pacini, and  genital corpuscles . No  Meissner's corpuscles  and few organized nerve endings are present. [ 14 ]  There are concentrations of nerve tissue in the area of ducts and masses of smooth muscle. The hair surrounding the areola adds additional sensory tissue. The mass of smooth muscle and glandular-duct tissue in the nipple and areola block the development of normal  dermal  nerve networks which are present in other erogenous regions and the development of special end organs. The entire breast has a network of nerve endings, and it has the same number of nerve endings no matter how large the  breast  is, so that larger breasts may need more stimulation than smaller ones.


Intense  nipple stimulation  may result in a surge in the production of  oxytocin  and  prolactin  which could have a significant effect on the individual's genitals, even to the point that some people of both sexes can achieve orgasm through nipple stimulation alone. Having the chest, breasts and nipples stimulated manually (hands, fingers) or orally (mouth, lips, teeth, tongue) is a pleasurable experience for many people of both sexes.


Many people find stimulation (kissing, biting, scratching, tickling, caressing) of the abdomen to be pleasurable, especially close to the pubic region. It can cause strong arousal in men and women, in some even stronger than stimulation of the genitals. The navel is one of the many erogenous zones that has heightened sensitivity. [ 15 ]  In a 1982 study of eroticism in dress entitled "Skin to Skin", Prudence Glynn claimed that the waist symbolized virginity and that it was the first place that a man would touch a woman "when indicating more than a formal courtesy". [ 16 ] [ 17 ]


The navel and the region below when touched by the finger or the tip of the tongue result in the production of erotic sensations. [ 15 ] [ 18 ]


The skin of the arms, and specifically the softer skin of the inner arms and across the creased mid-arm bend covering the ventral side of the elbow, are highly sensitive to manual or oral stimulation. Caressing with fingers or tongue, more vigorous kneading, and butterfly kissing can initiate arousal and, in some cases, induce clitoral/vaginal orgasm or penile ejaculation without direct contact with the latter areas. [ citation needed ]  The mid-arm bend is especially sensitive due to the thinner skin found there, which makes nerve endings more accessible.  [ citation needed ]  Arm sensitivity may be reduced or concentrated to a more narrow range by excessive muscularity or obesity on the one hand, or transformed to uncomfortable tenderness by excessive thinness on the other.


Some consider the armpits to be an erogenous zone, despite the similarity of the axillae (armpits) to normal-haired skin in both the density of nerves and hair follicles. Exaggerated or anticipated digital (fingers, toes) or oral (mouth, lips, tongue) stimulation is believed to be responsible for the heightened sensual response.


If  pheromones  exist for humans, they would likely be secreted by a mixture of liquid from the  apocrine glands  with other organic compounds in the body. [ 19 ]  George Preti, an organic chemist at the  Monell Chemical Senses Center  in  Philadelphia  and Winnefred Cutler of the  University of Pennsylvania 's psychology department, discovered that women with irregular  menstrual cycles  became regular when exposed to male underarm extracts. [ 19 ]  They hypothesized that the only explanation was that underarms contain pheromones, as there was no other explanation for the effects, which mirrored how pheromones affect other  mammals . [ 19 ]


The fingertips have many nerves and are responsive to very light touches, like the brushing of a tongue, light fingernail scratching or teeth stroking. The sides of the fingers are somewhat less sensitive and more ticklish. [ citation needed ]  Both light and firmer touches work well at the junction of the fingers. Human fingertips are the second-most sensitive parts of the body, after the tongue.


The  thighs  can be sensitive to touch.


An exaggerated tickle on the back of the legs and knees can also be sensitive for some.


Because of the concentration of nerve endings in the sole and digits of the human foot—and possibly due to the close proximity between the area of the brain dealing with tactile sensations from the feet and the area dealing with sensations from the genitals—the sensations produced by both the licking of the feet and sucking of toes can be pleasurable to some people. Similarly, massaging the sole of the foot can also produce stimulation. Many people are extremely ticklish in the foot area, especially on the soles.


Female copulatory vocalizations , also called  female copulation calls  or  coital vocalizations , are produced by female  primates , including  human females , and female non-primates. They are not purposeful, but instead are evolutionary and are spontaneously produced by female primates, including women, to encourage her partner to produce good-quality sperm during the mating process. Copulatory vocalizations usually occur during  copulation  and are hence related to  sexual activity . [ 1 ]  Vocalizations that occur before intercourse, for the purpose of attracting mates, are known as  mating calls .


In  primates , copulation calling is typically observed at the end of  mating [ 2 ]  and there are vast variations between species regarding its occurrence, frequency, and form. It is agreed that coital vocalizations fulfill an  evolutionary  purpose [ 3 ]  and that they serve as adaptive solutions to problems that the females face, such as  infanticide , as well as  obtaining high quality sperm . [ 2 ]


In non-primates, copulatory calling predominantly occurs before copulation in order to attract mates ( mating call ). Calls vary in  frequency  (14 Hz [ 4 ]  to 70,000 Hz [ 5 ] ) and function. One of the main purposes of females vocalizing is the induction of  mate guarding  behavior in males. [ 6 ]  Conversely, calls may also be used in order to attract high ranking mates who can prevent intercourse with the initial partner. [ 7 ]  This is done to incite  male mate competition .