Burned by SPF
Cancer
Beachgoers using sunscreen to prevent skin cancer might be rubbing themselves the wrong way--even if they are rubbing in lotion with a high SPF number like 30. SPF, or "sun protection factor," doesn't rate a type of sunlight that may play a crucial role in triggering cancer.
The danger light isn't sunburn red. It's a type of ultraviolet light called UVA, which seems to suppress your immune system and allow cancer cells to flourish. SPF numbers rate only protection from sunburn, caused mostly by another light type, UVB. But a hundred times as much UVA as UVB reaches Earth's surface. "Because there's so much more UVA, we find that the UVA wave band in sunlight is more important" to immune-system damage, says biologist Gary Halliday of the University of Sydney in Australia--a country of sun worshipers with the highest rates of skin cancer on the planet. There are compounds that block a lot of UVA, but you have to squint at the label to learn if your sunscreen has them. Don't rely on the large-lettered claims on the front of the bottle.
Scientists have recognized UVA's cancer-causing potential only in the past decade. Research has shown that mice can get skin cancer from UVA alone. In a study published this month in the Journal of Investigative Dermatology, Halliday and his colleagues smeared different sunscreens on people's backs and shined ultraviolet light on them. Among the group, skin slathered in sunscreens that blocked more UVA had immune cells--the anticancer guards--that remained the most active.
The fine print. While sunscreens may claim they block UVA, their protection from that light isn't as strong as their UVB protection, says Vincent DeLeo, chairman of dermatology at St. Luke's-Roosevelt Hospital Center and Beth Israel Medical Center in New York. Bottles that say "broad spectrum" or "UVA" on the front do block some UVA. How well they protect you depends on the whole formula, says biologist Patricia Agin of Coppertone, the sunscreen company. (Indeed, Halliday found the same UVA blockers doing both well and poorly in different sunscreen formulas.) Agin says your best bet is to make a choice based on ingredients. Zinc oxide blocks the widest range of rays from the UVA spectrum, and avobenzone, also called Parsol 1789, is also effective.
The Food and Drug Administration hasn't decided yet how to tell companies to test for UVA protection, though the agency plans to release new rules for testing and labeling in 2005. This summer, read labels carefully. Protective clothing and a wide-brimmed hat will be a big help, DeLeo says. Lots of sunscreen that's higher than SPF 15 can aid you a bit: UVA causes some burning, so high-SPF sunscreens do block some UVA rays. Don't forget, DeLeo says, to reapply it often.
This story appears in the July 21, 2003 print edition of U.S. News & World Report.
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