Deceptive Protection Sunscreens Prevent Sunburns, But Not Deadly Skin Cancer, Researchers Say

While sunscreens protect people from sunburn, they apparently don’t prevent the most deadly skin cancers and may also fail to prevent premature skin aging, researchers said Tuesday.

Even though use of sunscreens has risen significantly in the past decade, cases of melanoma skin cancer also have been rising, and researchers now question their earlier assumption that linked sunburns and cancer.

Speaking at the annual meeting of the American Association for the Advancement of Science, several researchers said people at high risk of melanoma cannot count on sunscreens to protect them.

Sunscreens could actually contribute to melanoma if their sunburn protection encourages sensitive people to stay in sunlight longer than they otherwise would, said Dr. Marianne Berwick, an epidemiologist at Memorial Sloan-Kettering Cancer Center based in New York.

“Based on the evidence, we conclude sunburn itself probably doesn’t cause melanoma, but it is an important sign of excessive sun exposure, particularly among those who are genetically susceptible because of their skin type,” Berwick said.

People with blond or red hair and light-colored eyes and who have numerous moles are genetically far more likely to develop melanoma than people with dark hair and fewer moles, Berwick said.

Sensitive people should avoid sun exposure and wear protective clothing when in the sun, she advised, but others can probably enjoy the sun with little fear.

Since 1973, the incidence of melanoma has increased by about 4percent a year, according to data compiled by the American Cancer Society. More than 41,000 cases are expected to strike in the United States this year, causing more than 9,000 deaths. Other types of skin cancer, while estimated to afflict more than a million Americans a year, rarely cause death.

Some scientists have speculated reduction of the ozone layer in the upper atmosphere may play a role in the increase in melanoma. But Richard Setlow, a senior biophysicist at Brookhaven National Laboratory based in Upton, N.Y., said his research suggests this is unlikely.

Setlow reported that while short waves of ultraviolet light called UVB cause skin to burn, it appears longer waves called UVA play a bigger role in causing melanoma.

Sunscreens block UVB, as does the ozone layer, but UVA sunlight passes through the ozone easily. Working with a hybrid tropical fish that lacks genes needed to prevent melanoma, Setlow has concluded 90 percent of sunlight’s melanoma-causing effects come from UVA.

Even sunscreens that claim to block UVA as well as UVB cannot be counted on to prevent melanoma in sensitive individuals, Setlow said.