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Yale: Sun damage continues, even after dark

By now, most people are aware that unprotected sun exposure is a bad, cancer-causing thing. We also hold two things to be true: That the melanin in our skin tans will protect us, and that getting out of the sun will limit the damage. According to new research out of Yale University, both assumptions may be false.

UV rays do their damage via cyclobutane dimer (CPD), a type of DNA damage that prevents the DNA’s information from being read properly by cells (picture it as bent pins on an iPhone plug). Previously, it was believed that the whole point of melanin, the pigment that gives skin its darker tone, protected against CPDs. In fact, it may do the opposite.

“If you look inside adult skin, melanin does protect against CPDs. It does act as a shield,” said Douglas E. Brash, clinical professor of therapeutic radiology and dermatology at Yale School of Medical. “But it is doing both good and bad things.”

As it turns out, melanocytes not only produced CPDs immediately, but continued to do so well after exposure to UV rays. In fact, half of all CPDs found in melanocytes were “dark” CPDs.

The explanation lies in something called “chemiexcitation.” When exposed to UV light, two melanocyte enzymes are activated such that an electron in melanin get’s “excited.” The resulting energy is then transferred to DNA in the dark, causing the same damage cause by the sun in daylight.

The silver lining is that this is a relatively slow process – people have several hours between sun exposure and night time before the chemiexcitation takes full effect. In theory, some sort of “after-hours” sunscreen analog may prove useful in warding off sun-related illnesses like skin cancer. No such thing presently exists, but researchers are hopeful that more information may one day spur development.

Thus ends your daily reminder to always wear sunscreen and avoid the sun at all costs.