When you think you've had enough sun, you probably move into the shade. But, according to a new study, that might not be soon enough -- because it turns out that sun keeps damaging skin for hours after exposure.
A team of scientists from Yale University have shown that sunlight does its damage to DNA over a protracted period of time. We already knew that the UV rays from the sun cause kinks in the DNA of skin cells called -- brace yourself -- cyclobutane pyrimidine dimers. These, let's call them CPDs, form in the DNA and go on to cause mutations and, sometimes, cancer. It was thought that the damages occurred when the UV light hit the DNA.
In experiments with mouse skin cells, though, the Yale team has carried out trials which show that skin cells continue to produce CPDs for up to three hours after they have been exposed to UV light. The experiments show that the effect is only observed in cells that contain melanin -- a skin pigment that's usually thought to shield against UV rays. But our skin cells contain melanin.
Further inspection has revealed that the UV light activates two enzymes which combine and then form an electron inside the melanin. The energy dumped into the melanin via this electron is then transferred to the DNA where, you guessed it, it causes the CPDs. Exposure to UV light seems to kick-start the enzymes, which then remain active for several hours. According to the researchers, the same process happens in human skin cells.
While it's far from good news, not least because it means we've probably been underestimating the true damage sun causes to our skin, there is some hope. The team suggest that it could be possible to block the effects of the enzymes using antioxidants.; indeed, in a Petri dish, the team have shown that ethyl sorbate does just that. That suggests that, with a little time and effort, it may be possible to create a sunscreen that quells the after-effects -- although it's likely a little way off. [Science via New Scientist]
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