Sunlight can cause cancer-related DNA damage hours after light exposure, owing to a skin pigment that was largely thought to be protective.
Douglas Brash at Yale University School of Medicine in New Haven, Connecticut, and his team studied how the pigment melanin in mouse skin cells responds to ultraviolet (UV) light. They found that UVA radiation, the main type of UV light that comes from the Sun and from tanning beds, creates melanin by-products that damage DNA, generating DNA derivatives called cyclobutane pyrimidine dimers (CPDs) for up to three hours after light exposure.
CPDs are associated with the skin cancer melanoma, so blocking their formation could be a way to develop sunscreens that can be used after exposure to sunlight, the team says.
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Sunlight damages DNA in the dark. Nature 518, 459 (2015). https://doi.org/10.1038/518459b