Sunlight Continues to Damage Your Skin Even After It Gets Dark

It turns out that sunlight continues to damage skin--even after it gets dark. Scientists have found that much of the damage that ultraviolet radiation (UV) does to skin occurs hours after sun exposure.

Exposure to UV light from the sun or from tanning beds can damage the DNA in melanocytes, which are the cells that make the melanin that give skin its color. This damage is a major cause of skin cancer, which is the most common form of cancer in the United States. In the past, researchers believed that melanin protected the skin by blocking harmful UV light, but there have also been studies that suggest melanin is associated with skin cell damage.

In order to get to the bottom of this issue, the researchers exposed mouse and human melanocyte cells to radiation from a UV lamp. The radiation caused a type of DNA damage known as cyclobutane dimer (CPD), which is when two DNA "letters" attach and bend the DNA, preventing the information it contains from being read correctly.

In this study, the melanocytes not only generated CPDs immediately, but continued to do so hours after UV exposure ended in the dark. Cells without melanin, in contrast, only generated CPDs during UV exposure. This study, in particular, shows that melanin has both carcinogenic and protective effects.

"If you look inside adult skin, melanin does protect against CPDs," said Douglas Brash, one of the researchers, in a news release. "But it is doing both good and bad things."

The findings are published in the journal Science.

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