PHILADELPHIA -- A presentation at a science conference Tuesday questioned the widely held belief that sunscreens lower the risk of deadly melanoma skin cancer, but specialists still caution against exposing the skin to sunlight without using a sunscreen.
Sunscreens prevent sunburns, and since there is evidence that frequent burns, especially at an early age, lead to melanoma, many experts assume that using sunscreens helps ward off skin cancer.
But melanoma cases have sharply risen over the last 25 years even as sunscreen use has become more common. Melanoma now strikes about 42,000 Americans a year, killing 7,300.
Dr. Marianne Berwick, an epidemiologist at Memorial Sloan-Kettering Cancer Center in New York, said her study and others offered no convincing evidence that using sunscreens prevented melanoma.
"It's not safe to rely on sunscreen," Dr. Berwick said.
Ten studies have looked at the question, she said at a meeting of the American Association for the Advancement of Science. Three, including her own, found no link between sunscreens and the risk of melanoma. Two suggested that sunscreens seemed to prevent melanoma.
The five others found that the risk of melanoma increased among sunscreen users, probably because people who use sunscreens most are already at highest risk because of a light complexion.
Several dermatologists strongly disagreed with Dr. Berwick's report.
Until there is clear proof that sunscreens are ineffective, Dr. Darrell Rigel of New York University said, "it would be irresponsible to discontinue all recommendations about using sunscreens."
Melanoma may take 20 years or more to develop after excessive sun exposure. Some doctors argue that it is simply too soon to prove that sunscreens are helping, since No. 15 sunscreens and stronger ones have been in wide use only since the mid-1980's.
Dr. Roger Ceilley of the University of Iowa, president of the American Academy of Dermatology, said most of the people now getting melanoma were exposed long before they began using sunscreens. "I personally think it very likely reduces the risk of melanoma," Dr. Ceilley said. "I use it every day and recommend it to my patients."
Dr. Jouni Uitto of Thomas Jefferson University in Philadelphia said most skin specialists would agree. "If you asked 100 dermatologists," he said, "95 would say sunscreen protects against melanoma, and they counsel their patients that way."
Still, these doctors cautioned against using sunscreen as an excuse to bake in the sun. They said people at high risk of melanoma should avoid prolonged sun exposure, stay out of the midday sun and wear hats and long-sleeve shirts.
Generally, dermatologists agree with Dr. Berwick's contention that genetic susceptibility is the most important factor in melanoma. Her study, based on 1,200 people in Connecticut, found that fair-skinned people who burn easily are about six times more likely than darker people to get melanoma. And people with many moles have about six times the risk of people with few moles.
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