How does sunscreen help prevent skin cancer?

No. It causes skin cancer. Nature creates healthy things and man creates cancer causing things.

http://www.phifoundation.org/articles.ht...

It blocks the sun U.V. (ultra violet) rays from burning your skin. ultra violet is know to cause skin cancer.

I'm not quite sure, but I think it has something in it that doesn't let all of the sun's UV Rays burn your skin off.

Otherwise you'd be a burnt sausage in no time ;-P

It creates a layer on your skin so that the sun's ultra-violet rayes cannot pass through.

Because of the chemicals in sunscreen your body is protected from the deadly rays of the sun

Most but not all sunscreens cause cancer.

Most of the body's vitamin D supply, about 75% of it, is generated by the skin's exposure to UVB rays. Using a sunscreen drastically lowers the cutaneous production of vitamin D3. A low blood level of vitamin D is known to increase the risk for the development of breast and colon cancer and may also accelerate the growth of melanoma Although the medical establishment still strongly supports the use of sunscreens there is a growing consensus among progressive researchers that the use of sunscreens does not prevent skin cancer and, as a matter of fact, may promote skin cancers as well as colon and breast cancer.

It is my understanding that most sunscreens protect from UVB radiation and not from the UVA rays which penetrate deeper. Thus their high SPF ratings create a false sense of security in those using these products and this may actually increase the risk of skin cancer by causing longer exposure to UVA radiation. On the other hand titanium dioxide, which is considered to be a natural physical barrier type sunscreen, is thought to provide total protection with broad-spectrum blocking capabilities that include UVA, UVB and UVC radiation. Some believe that for anyone concerned with total protection, use of this mineral shield should be part of their cosmetics, skin lotions and, of course, sunscreen. So look for sunscreens that contain titanium dioxide.

There are two other key factors that you should be seeking in sunscreens. One is the addition of natural sun protectors and the other is the absence of potentially harmful and unnecessary ingredients or contaminants that could be unhealthy.

For example, although Coppertone庐 Shade and Neutrogena庐 Sunblock products block UVA/UVB radiation, they also contain triethanolamine (which can cause formation of undisclosed cancer-causing nitrosamines in some products) and methylparaben, a preservative now known to imitate the effects of the female hormone estrogen.

For those consumers who seek excellent protection and demand the highest quality, Aubrey Organics produces one of the very best lines of all-natural sunscreens. Not only do their sunscreen products avoid use of suspect ingredients, they combine UVA-protective titanium dioxide with Padimate O for a full-spectrum blocking effect. In addition, these products contain much higher amounts of powerful skin protecting herbs and nutrients.

In July 2007, UV Natural ranked as the Safest and most effective sunscreen sold in the US / World. Beating nearly 800 other brands, UV natural is recognized as offering uncompromising safety and efficacy in sun protection.

MelanSol claims to be a 100% natural sunscreen product, Also at puresunscreen.com where MalanSol is featured it says regarding MelanSol: "The question I hear most often is, 鈥淵ou only go as high as SPF-18鈥? I want to tell you a little secret. Contrary to what you have been led to believe, lathering on a higher SPF doesn鈥檛 mean that will gain that much more protection. A traditional SPF of 30 will filter 98 percent of UV rays verses the 95 percent filtering you get from our MelanSol庐 SPF-18. You don鈥檛 really need more because, contrary to what you were led to believe, the sun is actually good for you! There are numerous health benefits to be had from exposing yourself to the sun. They key is pace your exposure! Check out this article entitled 鈥淭oo much Sunscreen?鈥? see the last link posted below

Please note: Most of the above info is copied from the links below.

Whether sunscreen does prevent skin cancer or not is actually a subject of fierce debate right now. Unfortunately the opinions of the sunscreen skeptics are far underrepresented in the popular press - probably due to the financial interests of the cosmetic industry.
First of all: skin cancer and sunburn are caused by totally different mechanisms. Sunburn is caused by the direct DNA damage that is triggered by UVB. In contrast the malignant melanoma - which causes most fatalities - is nearly exclusively caused by the indirect DNA damage that stems from free radicals. Many sunscreens prevent the direct DNA damage but they increase the amount of free radicals.
Sunscreen is supposed to stay on the surface so that it does not get in contact with living tissue. Unfortunately a small fraction of the chemical substances always penetrates through the epidermal barrier with time. When sunscreen molecules are in contact with living tissue and then they are excited they become very reactive and the free radicals that are produced damage the DNA.
All this is happening even so the sunburn (direct DNA damage) is prevented.
Free radicals cause cancer.
The cosmetic industry has used substances like benzophenone, psoralen, coumarin, TiO2. All these substances are known to be photosensitizers for harmful reactions. This means that they amplify the production of free radicals from UV-light.
The molecules that remain on the surface of the skin filter the UV light and thereby reduce the skin cancer risk, but even small amounts of these substances - as little as 1% of the applied sunscreen - is enough, to increase the amount of free radicals. This has been measured in several experiments.
In agreement with this lab-data the medical statistics show an increased melanoma risk for sunscreen users compared to non-users. See wikipedia: "sunscreen"