Skin Damage Possible Even in the Dark

When we think of skin cancer, sunlight usually comes to mind. But an interesting new study reveals that skin damage is possible even in the dark, leaving no place safe.

It is true that exposure to ultraviolet radiation (UV) light from the Sun or from tanning beds can wreak havoc on your skin. Specifically, it damages the DNA in melanocytes - the cells that make the melanin that gives skin its color. This UV damage is a major cause of skin cancer, the most common form of cancer in the United States.

However, new research published in the journal Science discovered that much of the damage that UV does to skin occurs hours after sun exposure.

Previous research has suggested that melanin protects the skin by blocking harmful UV light, but now it appears that it can do harm as well as good.

In the study, a team led by researchers at Yale University exposed mouse and human melanocyte cells to radiation from a UV lamp. The radiation caused a type of DNA damage known as a cyclobutane dimer (CPD), in which two DNA "letters" attach and bend the DNA. This prevents any information it contains from being read correctly.

Surprisingly, the melanocytes not only generated CPDs immediately, but also continued to do so hours after UV exposure ended. Cells without melanin generated CPDs only during the UV exposure.

"Melanin may thus be carcinogenic as well as protective against cancer," the researchers wrote.

"If you look inside adult skin, melanin does protect against CPDs. It does act as a shield," lead study author Douglas E. Brash added in a statement. "But it is doing both good and bad things."

In addition, to their astonishment, Brash and his colleagues found that half of the CPDs in melanocytes were "dark CPDs" - CPDs created in the dark. This is because of a process called chemiexcitation, during which UV light activates two enzymes that combined to "excite" an electron in melanin. The energy chemiexcitation generates is transferred to DNA in the dark, creating the same DNA damage that sunlight caused in daytime.

While this news does not bode well in the fight against skin cancer, researchers do hope to combat UV's after-dark effects in the future with new preventive tools, such as an "evening-after" sunscreen designed to block the energy transfer.

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