Sunlight Damages Skin Hours After Exposure

Much of the skin damage caused by UV radiation may not develop until hours after a patient has been exposed to sunlight, according to a recent study. The study, published in Science, exposed mouse and human melanocytes, the cells responsible for the production of melanin, to radiation from a UV lamp. This radiation caused a cyclobutane dimer (CPD), a form of DNA damage in which the DNA becomes “bent” and unreadable. Although some CPDs formed immediately, the researchers found that half of the CPDs were “dark,” having been generated hours after the melanocytes were exposed to UV light.

The research team discovered this damage was possible due to a process known as chemiexcitation, in which UV light activates 2 enzymes that combine to “excite” an electron in melanin. The energy generated from this process can transfer to DNA in the dark, damaging DNA in the same way as sunlight. The researchers also found, however, that the 1 group of cells to undergo this process were those with melanin, indicating that melanin could have a carcinogenic effect in addition to protecting the skin from harmful UV light. Although the study authors acknowledged that this finding was concerning, they added that the slowness of chemiexcitation may allow for the application of new preventive tools, such as an “evening-after” sunscreen that would block the energy transfer.