If you’ve ever left the beach without a suntan only to find it showing up hours later, you may wonder why. Now a new study from Tel Aviv University has a possible answer.

The study, which was published in the Journal of Investigative Dermatology, says that how people tan has to do with the way the body attempts to protect itself from exposure to ultraviolet (UV) radiation, which most commonly comes from the sun or tanning beds, according to the Centers for Disease Control and Prevention (CDC).

It’s this UV radiation that causes skin to tan for some people in the first place. While many people may desire the tanned look, it’s actually a sign that the skin is damaged and attempting to repair itself.

“We have two mechanisms designed to protect the skin from exposure to dangerous UV radiation,” said Nadav Elkoshi, one of the authors of the study, in a news release. “The first mechanism repairs the DNA in the skin cells damaged by the radiation, while the second mechanism involves increased production of melanin, which darkens the skin in order to protect it from future exposure to radiation.”

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