How does sunscreen block the UV rays?
368794
The principal ingredients in sunscreens are usually aromatic molecules conjugated with carbonyl groups. This general structure allows the molecule to absorb high-energy ultraviolet rays and release the energy as lower-energy rays, thereby preventing the skin-damaging ultraviolet rays from reaching the skin.
26575
Ultraviolet Radiation, electromagnetic radiation that has wavelengths in the range between 400 nm, the wavelength of violet light, and 15 nm, the length of X rays. (The nanometre, nm, equals a millionth of a millimetre, or 40 billionths of an inch.) Ultraviolet radiation is produced artificially by electric arc lamps. Natural ultraviolet radiation is produced principally by the Sun.\n\nUltraviolet radiation can be harmful to living things, particularly when the wavelengths are small. Ultraviolet radiation with wavelengths below 300 nm is used to sterilize surfaces because it kills bacteria and viruses. In humans, exposure to ultraviolet radiation of wavelengths under 310 nm can cause sunburn; prolonged exposure over many years can cause skin cancer.\n\nThe Earth's atmosphere protects living organisms from the Sun's ultraviolet radiation. If all the ultraviolet radiation produced by the Sun were allowed to reach the surface of the Earth, most life on Earth would probably be destroyed. Fortunately, the ozone layer of the atmosphere absorbs almost all of the short-wavelength ultraviolet radiation, and much of the long-wavelength ultraviolet radiation. However, ultraviolet radiation is not entirely harmful; a large part of the vitamin D that humans beings and animals need for good health is produced when the skin is irradiated by ultraviolet rays.\n\nWhen exposed to ultraviolet light, many substances behave differently than when exposed to visible light. For example, when exposed to ultraviolet radiation, certain minerals, dyes, vitamins, natural oils, and other products become fluorescent—that is, they appear to glow. Molecules in the substances absorb the invisible ultraviolet light and are energized, then shed their excess energy by emitting visible light. See Luminescence. As another example, ordinary window glass, transparent to visible light, is opaque to a large range of ultraviolet rays, particularly those with short wavelengths. Special-formula glass is transparent to the longer ultraviolet wavelengths, and quartz is transparent to the entire naturally occurring range.\n\nUltraviolet astronomy has been carried out since the early 1960s with the aid of detectors on artificial satellites, providing data on stellar objects that cannot be obtained from the Earth's surface. An example of such a satellite is the International Ultraviolet Explorer, launched in 1978.
71055
Same as the black stuff under the eyes of baseball players, and players in other sports - it cuts down on the glare from anything shiny - mainly, the sun.  It helps the visibility, so you can make the play.
235390
because of the ultraviolet rays.
403501
I can attest to the fact that sunglasses really help. My grandmother who lived in the Philippines for most of her life (it's very hot and often sunny there), had to get her eye checked for cataracts several years ago. I went with her, and while the doctor was looking at her eyes, he told me that it was very obvious that my grandmother grew up where there was a lot of sun. \n\nThe cataracts was not caused by not wearing sunglasses, mind you. I just want to be clear about that.\n\nAs far as sunblock. Yes, it does help. Have you seen people who sunbathe a lot? Their skin looks kind off wrinkly and old. If the sun can do that to you, then it only stands to reason that sun block should offer some protection.
432601
the UV waves cause heterolytic fission of chemical bonds creating "radicals" which are very reactive species.  They will react with pretty much anything.  The UV radiation is therefore breaking down the skin and the colour molecules in paint and clothes, making them look like they are losing their colour.  The purpose of sun-tan lotion is not only to stop the UV radiation getting to your skin, but also to mop up all the free-radicals formed before they do any damage.  Skin cancer is caused by this process.  You are essentially changing the structure of the skin.
51917
What probably ages the skin most is the UVA and B sun rays.  After taking a good one-a-day vitamin formulated for your age and sex, to insure you are getting at least the minimum required amounts of essential vitamins from your diet as supplimented, consider using a dermatologist approved skin lotion with perhaps SPF 15 sunscreen protection.  If you block the sun with sunscreen, be sure to take enough Vitamin D, to make up for lost Vitamin D, usually received from sun exposure.\n\nDrug stores should have a suitable product such as Lubriderm - Daily UV Lotion.  Read the instructions and keep it out of the eys and away from children.  Good luck.
521234
It's called "melasma" or "mask of pregnancy." You'd want to use a physical sunblock (titanium dioxide based or zinc oxide based) while in the sun.
492110
I protect myself by staying inside when it's cold or rainy and I always wear sunscreen.\n\n:)
1047935
UVA:\nCan pass through window glass.\nIs not affected by a change in altitude or weather.\nIs present all day and every day of the year.\nPenetrates deep into skin layers.\nIs 5% of the sun's rays.\nIs 20 times more abundant than UVB rays.\nAffects long-term skin damage.\n\nUVB:\nCannot pass through window glass.\nCauses sunburn.\nCauses tanning.\nHelps the body with normal vitamin D production.\nVaries with the season. It is more intense in the summer than in the winter.\nVaries with weather conditions.\nIs more intense at midday than in the morning or late afternoon.\nIs more intense at high altitudes and near the equator.\nIs 0.5% of the sun's rays.\nIs protected against by the sun protection factor (SPF) in sunscreens.\nIs related to more than 90% of nonmelanoma skin cancer.\nIs related to cataracts.\n\nMore:\n\nHow Sunlight Works\n\nSunlight arrives on earth in three forms: infrared (heat), visible light and ultraviolet. Ultraviolet light is classified into three categories: \nUVA (315 to 400 nm), also known as black light, which causes tanning \nUVB (280 to 315 nm), which causes damage in the form of sunburn \nUVC (100 to 280 nm), which is filtered out by the atmosphere and never reaches us. \n99% of the sun's UV radiation at sea level is UVA. It is the UVB that causes most of the problems related to sun exposure: things like aging, wrinkles, cancer and so on, although research is increasingly implicating UVA as well. \nOne of the interesting things about UV radiation is that it is reflected by different surfaces. These reflections can amplify the effects of UV exposure. For example, snow reflects 90% of UV light. That is why you can get snow blindness and severe sunburns from skiing on a sunny day. Sand can reflect up to 20% of UVB that hits it, meaning that you can get extra UV exposure at the beach. \n\nOn the other hand, certain things absorb almost all UV radiation partially or completely. Glass is one of these substances - many glasses are very good absorbers of UV (which is why you may have heard that you cannot get sunburn in a greenhouse - just make sure it is glass and not plastic covering the greenhouse!). Most sunscreens use chemicals that have the same UV-absorbing properties.
391068
Do NOT ingest sun screen. There are chemicals and other ingredients that are way harmful to the body. The only way to make your skin more sun repellent is to use a higher SPF.
730561
the answers are\n1) True, opaque materials are those which donot allow light to pass through them. they block the path of light. so u cant see through them.\n\n2) True, sunscreens protect from UV rays by reflecting the photons of  UV wavelength, which are harmful, when exposed to the skin.\n\n3) True, the colour of any object is decided by which wavelength it reflects. cyan reflects the wavelength corresponding to blue and absorbs all other wavelengths.\n\n4) False, because light waves are also diffracted and there are many applications on diffraction of light too.\n\n5) False, because lenses are for converging or diverging light rays, but not to reflect them.
541675
The SPF (Sun Protection Factor) of a sunscreen indicates the time period you can stay in the sun without burning based on your skin complexion. The higher the number the longer you can remain in the sun. Dermatological recommended means the sun screen will be easier on the skin.
536038
Their are people that live in areas where they are exposed to sun every day for long periods time and never develop skin cancer. I believe that it is the ingredients that are put into lotions and sun blockers that actually cause skin cancer. The people that live in those areas do not use protection.
709759
The chemical benzylhydroquinone \nin some plastics is absorbed through the skin and inhibits the production of melanin.
528886
Nudists work up a tan just like anyone else. Sunscreen, exposure and shade when their skin has had enough sun. But because they don't wear clothes unless nature or society outside their group requires it, nudists also get wind burned which helps keep their skin tanned so they can withstand more sun.\n\nThink about driving your car with your window down on a cloudy day. You are wearing a t-shirt and your arm is resting in the window. Even though the sun is hidden behind clouds you can still end up with your arm looking sun burned from exposure to the wind.\n\nThe combination of sun and wind can keep their skin tanned longer so they don't need as much protection as a non-nudist does.
501110
The sun glasses are coated with a film that filters out the Sun's ultraviolet rays and prevents them from reaching and damaging the eyes.\nA must-have feature for all sunglasses is complete (100 percent) protection against the potentially damaging effects of the sun's ultraviolet-A and ultraviolet-B rays. Avoid buying dark sunglasses that do not offer 100 percent UV protection. Dark glasses prompt the pupil of the eye to dilate (enlarge), allowing UV rays to enter. So, if dark glasses lack complete UV protection, they can promote damage to the eye.