Do you find yourself constantly longing to soak up the sun? It might be about more than seeking that killer tan. A new study suggests sunbathing can actually become a kind of addiction.

As reported by New Scientist, David Fisher at Harvard Medical School and Massachusetts General Hospital in Boston showed that mice responded to UV light exposure with chemical response and behavior similar to those with drug addiction.

The finding could have significant implications since UV exposure is a known cause of skin cancer -- the leading kind of cancer in the United States. More than 3.5 million skin cancers in over two million people are diagnosed annually, according to the Skin Cancer Foundation.

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For their study, Fisher and his colleagues gave mice a shave and then exposed them to UV light for five days a week. Each session was comparable to a fair-skinned person sitting in hot, Florida sun for 20-30 minutes.

After six months they noticed something peculiar. At the start of the study, the mice produced more feel-good hormones called beta-endorphins, which bind to opioid receptors – the same receptors at play with heroin addiction. Toward the end of the study, however, their levels of the beta-endorphins dropped (as evidenced by their decrease in pain tolerance).

Fisher said this suggests that the mice were building up a level of tolerance to the UV exposure. In other words to produce the same beta-endorphin-boosting effect, the mice required more time in the UV light. The scenario is similar to addicts who require more of their drug to achieve the same high.

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The mice also displayed some classic signs of withdrawal behaviors including shaking, tremors and chattering teeth.

As Fisher told New Scientist, "We have a propensity towards seeking the most common carcinogen in the world."

Do we really all carry the potential to become sun addicts? The notion makes some evolutionary sense since our bodies require vitamin D and require some sun in order to synthesize the vitamin.

Some health experts, however, take exception to the comparison between overdoing it in the sun and becoming hooked on heroin.

"Even if an individual truly has no control over their compulsive behavior – even if they experience highs and lows, tolerance and withdrawal – that doesn't necessarily make someone an addict," cautioned Carlton Erickson, who works on addiction at the University of Texas at Austin.

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Fisher argues that however we define the body's response to UV light exposure, his results suggests that the tanning bed industry should be more closely regulated.

"Tanning salons are allowed to offer deals or free trials that get teens hooked. It's a great business model for them, and a fairly devastating model in terms of human health."

The research was published in the journal Cell.