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Despite warnings about the dangers of the sun's ultraviolet rays, some people continue to bask in the sunlight. In a new study, researchers set out to examine why and how people become addicted to the sun. After conducting experiments on mice models, the team discovered that UV radiation could trigger the release of endorphins, also known as "feel-good" hormones.

"This information might serve as a valuable means of educating people to curb excessive sun exposure in order to limit skin cancer risk as well as accelerated skin aging that occurs with repeated sun exposure," said senior study author David Fisher of Massachusetts General Hospital and Harvard Medical School. "Our findings suggest that the decision to protect our skin or the skin of our children may require more of a conscious effort rather than a passive preference."

Fisher and his colleagues examined the effects of UV radiation on mice by shaving a group of mice and exposing them to UV light for six weeks. Another group of mice acted as the control and was not exposed to sunlight. The researchers found that within one week, the mice's levels of endorphins measured in their bloodstream increased.

After six-weeks, the team looked for any signs of addictive behaviors by giving the mice an opioid-blocking drug. The researchers explained that endorphins might lead to feel-good emotions because they activate opioid receptors that relieve pain. Drugs, such as morphine and heroin activate opioid receptors as well. They found that mice that were exposed to UV radiation exhibited signs of withdrawal, such as teeth chattering, tremors and shaking whereas mice that were not exposed to UV radiation were unaffected.

"It's surprising that we're genetically programmed to become addicted to something as dangerous as UV radiation, which is probably the most common carcinogen in the world," Fisher stated in the press release. "We suspect that the explanation involves UV's contribution to vitamin D synthesis in the skin. However, in the current time, there are much safer and more reliable sources of vitamin D that do not come with carcinogenic risk, so there is real health value in avoiding sunlight as a source of vitamin D."

The study, "Skin B-endorphin mediates addiction to ultraviolet light," was published in Cell.