The parallel rise in skin cancer and sunscreen use has prompted chemists to reexamine the behavior of the products' active ingredients. Because sunscreens absorb light energy and must then release it in some form, they may deliver damaging ultraviolet (UV) radiation to sensitive cells. That raises the troubling, but unproved, possibility that sunscreens may have a hand in promoting skin damage. To learn more, chemists are testing sunscreens' responses to UV light. "Since [sunscreens] are so widely used, it is important to know as much as possible about them," says John Know-land of the University of Oxford in England.
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