As long as we’ve known the sun to be harmful, we’ve associated sunbathing with cancer. New evidence, however, suggests the risk is just as real in complete darkness. Why? Because melanin – our protector, is also a wolf in sheep’s clothing.

What’s more, most of the damage to skin actually occurs in the dark, contrary to long-held beliefs.

The Yale team leading the research started off with the simple assertion that exposure to ultra-violet rays damages the DNA in melanocytes, the cells that make up melanin, the pigment that gives skin its color. Too much exposure results in the most common form of skin cancer in the United States.

But while in the past we tended to view melanin as a sort of protection shield against UV rays, the researchers found that it’s actually associated with skin cell damage. The tests showed it to be both benefactor and malefactor, fighting cancer and helping create it.

"If you look inside adult skin, melanin does protect against CPDs. It does act as a shield," Professor of therapeutic radiology and dermatology Douglas E. Brash says. "But it is doing both good and bad things."

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The DNA damage this causes is known as cyclobutane dimer (CPD). It normally causes two ‘letters’ of a DNA strand to entangle together, preventing genetic information from being read normally. As expected, CPD followed in both examples. However, cell degeneration was taking place hours after exposure as well, the Yale team found. By contrast, cells without melanin were only affected by CPD during UV exposure.

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To test the findings further, Brasher and his team prevented DNA repair in mice with damaged cells, texting the extent of true damage. What they found was clear proof: half of the melanocytes they saw were created in the dark, after exposure.

But what was the reason for this? Brash’s associate on the research, Sanjay Premi, discovered that the reaction created by UV rays leads to two enzymes combining and “exciting” a particular electron in melanin. This process creates a type of energy known as chemiexcitation.

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And that energy transfer only happens in the dark. The reason science didn’t address the issue before is because we’ve only known chemiexcitation to happen in lesser animals and lower plant life.

However, it would also appear that the process can be mitigated, for it occurs as a reaction to something that happened before. So, according to Yale, there’s no reason we can’t prepare for it by applying special lotions designed to prevent chemiexcitation from taking place.