How Sunlight Damages the Skin – in the Dark

Skin damage usually goes hand-in-hand with sun exposure. But what if skin damage also occurred in the absence of light? A recent study indicates that this might be the case.

UV Lights, Mice and People

This report, spearheaded by researchers from Yale University, found that ultraviolet (UV) radiation can inflict damage on the skin hours after exposure. Appearing online in the journal Science, this report based its findings on damage observed in both mouse and human DNA. The study identified a rather surprising culprit behind this connection –

Previous research had reached a far different conclusion regarding melanin, arguing that that this skin pigment acted as a sort of shield against the sun’s rays. The Yale team, in contrast, determined that UV light has a negative effect on the DNA of melanocytes, the cells responsible for giving melanin its distinct colors.

With the aid of a UV lamp, the Yale researchers exposed both mice and human melanocyte cells to significant amounts of radiation. When hit with this radiation, the study authors noted that the DNA samples took on a bent shape, a reaction referred to as cyclobutane dimer (CPD). Consequently, the information contained by this DNA cannot be
properly read.

Sunscreen at Night?

What stood out to the Yale team was that these DNA samples were not just damaged immediately after being hit with radiation; instead, the study found CPDs continued to appear hours after radiation exposure had ceased. The mouse cells revealed another interesting discovery; about one half of CPDs in this set of samples formed after the radiation exposure period.

So what could explain these findings? One of the study’s contributors, Sanjay Premi, contends that the UV light stimulated two enzymes within the cells, resulting in an activity spike within the melanocyte cells. During the post-exposure hours, this energy affixed itself to the cell’s DNA, leading to the appearance of troublesome CDPs.

If there is a silver lining to this study, it is the fact that these “dark” CDPs take hours to form. Because of this trait, an “evening-after” sunscreen could theoretically be used to prevent DNA damage within melanocytes.

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