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Scientists testing mysterious link between sunscreen, skin cancer

Question: I heard on the news the other day that sunscreens may not be as protective as we thought and may actually cause skin damage. Do sunscreens work? Should I continue using them on my children?

Answer: Sunscreens do help prevent sunburn by absorbing ultraviolet radiation. Anyone who has ever used sunscreen would have to agree that it works. In addition, the diligent use of these products prevents premature skin aging _ where the skin yellows, wrinkles, dries, sags and gets blotchy. A striking illustration of this appeared in the Journal of the American Academy of Dermatology. Dermatologists evaluated the facial skin of two groups of women, 19 to 51 years old, who had lived in Arizona for at least 10 years. One group was exposed to the sun fewer than two hours a week and the other, more than 12 hours a week. The women were photographed. Then a third group of women was shown the photos and asked: "How old do these women look?" These judges overestimated the age of the older women (those over 40) with the higher skin exposure by six to 10 years.

We are also told that sunscreen will protect us from skin cancer. It's this claim that is being questioned, most recently at the February meeting of the American Association for the Advancement of Science. At issue was the suggestion that instead of preventing skin cancer, sunscreen may be encouraging the disease. This concern arose because studies are showing a significant rise in skin cancer at the same time that the use of sunscreens has increased dramatically. For example, sunscreen use has risen 19 percent in the past decade. And the number of new cases of most cancers is declining in the United States _ with one notable exception, sun-induced skin cancer. At the current rate, one in seven of us will develop some form of the disease in our lifetime, and one in 100 will develop melanoma, the potentially deadly kind.

The AAAS scientists discussed two theories for explaining this trend. One has to do with a possible adverse chemical reaction between the sun and sunscreen. As sunscreen absorbs UV radiation and prevents sunburn, the energy involved in the process may cause damage inside the skin cells, which, over time, could lead to skin cancer. The other theory, which is more likely, is simply that more of us are using sunscreen to stay in the sun longer. The conclusion from the AAAS meeting was that until more is known, we should all continue using sunscreen and taking other measures to minimize sun exposure.

Protecting children: The effects of being burnt by the sun are cumulative. Our skin "remembers" each exposure. And its memory is good _ going all the way back to childhood. With this in mind, here are a few basic precautions.

+ Children under the age of 6 months should never be in direct sunlight. If this is unavoidable, talk to your pharmacist about sunscreen use and about formulas for children that have less "sting."

+ The sun's rays are strongest between 11 a.m. and 3 p.m., so try to limit exposure at that time.

+ Use sunscreen with at least an SPS of 15 and apply it about 20 minutes before going outside to allow time for the protective chemicals to be absorbed into the skin.

+ When going out into the sun, youngsters should be covered up as much as possible, including a hat. Keep in mind, too, particularly when at the beach, that it is possible to burn under loose-weave clothing (like light T-shirts) and open straw hats.

+ Older girls should be encouraged to apply their makeup over a sunscreen. This does not decrease its protective effect. Incidentally, there are facial-only sunscreens that are less oily and suggested for acne-prone or sensitive skin.

+ Teenagers particularly should be informed that water-resistant sunscreens are only good for about 40 minutes of water activity, and those labeled waterproof are effective for about 80 minutes. As a general rule, regardless of the type, sunscreen should be applied every hour when in the open, and more frequently if swimming. Also, it's important to make the point that a tan provides zero protection from the destructive rays of the sun.

Warning: Don't cook

your cutting board!

Last week's column suggested microwaving wooden cutting boards as a way to kill germs on and below the surface of the wood, information from a study published in the Journal of Food Protection. After a reader called to report that her board started smoking after only two minutes in the microwave, Dr. Bird tried it himself and got the same results. He suspects the problem may be laminate or glue used in some cutting boards, the presence of which you can't always detect. "Readers should not try this," he warns. He apologizes for the misinformation.

Patrick J. Bird, dean of the College of Health and Human Performance, University of Florida, draws on a data base of more than 3,800 medical, health and fitness journals in preparing answers to questions in his column. Write with questions to Dr. Bird, College of Health and Human Performance, University of Florida, Gainesville, FL 32611.