Simply slapping on some sunscreen may cause more harm than good, according to a study due to be published in New Scientist later this month.

Research carried out at the University of California found that if people apply sunscreen less than once every two hours they might be better off not using any at all due to the effect of free radicals.

Kelly Hanson, a university chemist, along with her colleagues tested three UV filters commonly found in sunscreens. After one hour they found that each compound had sunk into the skin meaning its protective effect was greatly reduced.

Worse, they found that the samples contained more reactive oxygen species than skin exposed to UV with no sunscreen on it. Reactive Oxygen Species are free radicals that can damage skin cells and increase the risk of skin cancer.

Skin cancer charities already recommend that people go no more than two hours without reapplying. Our findings tend to support that, says Hanson, and suggest that it may actually be necessary to reapply even more often.

The team also propose that antioxidants, such as vitamins C and E, could be added to sunscreens. “In previous work we’ve shown that antioxidants can help neutralise reactive oxygen species in the skin,” says Hanson.

 Free Radical Biology and Medicine, DOI:10.1016/j.freeradbiomed.2006.06.011

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