Skin cancer is the most common form of cancer in the United States, and UV-seeking behavior is a major risk factor. Many UV seekers meet clinical criteria for a substance-related disorder, but the mechanisms underlying such an addiction have been unclear. One potential clue is that UV exposure stimulates the production of endorphins, which relieve pain by activating opioid receptors through the same pathway activated by prescription painkillers, morphine, and heroin.

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