Answer to Question #267 Submitted to "Ask the Experts"

Q

If we use sun block to protect us from the various types of UV rays are we safe from skin cancer? How effective is our sunblock? What is the mechanism behind sunblock?

A

Sunblock will help mitigate exposure to UV rays, but is not totally effective in preventing skin cancer. One of the primary reasons is that it wears off and needs to be reapplied. If sunscreen is not applied often enough, it may give a false sense of security leading to even more time in the sun. The more opaque the sunscreen the better. Not all sunscreens are equally effective. Some sunscreens are manufactured to block short-wave ultraviolet (UVB) radiation, which damage the skin's surface and cause redness and burning. Yet it is the longer wave ultraviolet (UVA) radiation that penetrates deeper into the skin. Unfortunately, UVA radiation is less likely to cause noticeable sunburn symptoms, even though it severely damages the elastic fibers and collagen and is significant in producing malignant melanoma. The best sunscreens block both UVB and UVA rays. Both avobenzone and benzophenone are good UVA blockers. For maximum benefits, sunscreen must be applied evenly to cool, dry skin 30 minutes before sun exposure. Waterproof and water-resistant sunscreens are best since effectiveness is not reduced by perspiration. Several Web sites found with a search for skin cancer give additional information on the effectiveness of sunscreens. Ken Barat Lawrence Berkeley National Laboratory