Summer brings with it flocks of families and friends to beaches and pools to cool off from the hot weather and enjoy a nap in the sun. It may be more instinctual than fun-loving urges that bring us outside, though: Last week, a study published in Cell linked soaking up the suns rays with a physiological response similar to that of other addictive substances.

Dr. David Fisher and his colleagues at Harvard Medical School and Massachusetts General Hospital exposed partially-shaved mice to UV light five times a week for six months. The amount of UV radiation was equivalent to a fair-skinned person sunbathing for 20 – 30 minutes, and caused the mice to produce melanin, the pigment-darkening chemical that protects skin cells from UV damage. Surprisingly, scientists noticed that melanin production also led to the production of a neuropeptide called beta-endorphins. Beta-endorphins block pain and bind with opioid receptors in the brain, spinal cord and digestive tract where drugs like heroin are also registered. As the study continued, the mice began to show signs of lower levels of beta-endorphins with the same level of exposure meaning they were developing a tolerance for UV rays. When the scientists stopped the UV treatment altogether, the mice showed symptoms typically associated with withdraw, including tremors and teeth chattering.

This finding could imply that humans may have a similar biological response we spend time outdoors in the sun’s rays. Many sensationalist headlines have already jumped to the conclusions that the physiological addiction to UV rays may be yet another detriment to our health from sun exposure.

It’s true that UV rays are a known carcinogen, and yet rates of the most aggressive form of skin cancer, melanoma, increase an average of 3 percent each year. Melanoma, other skin cancers and sunburn are caused by UVB rays of light, which measure between 280 – 315 nanometers in length. Though UVB rays make up only a fraction of the sun’s emissions, sunscreen primarily provides protection against these rays alone. UVA rays are slightly longer, measuring in between 315 – 400 nm, and trigger melanin production over time. These rays are what make us tan (and eventually wrinkly and leathery), and have popular cosmetically appealing affects. Those newly concerned about the possible addictive properties of UV rays, however, may consider paying for either sunblock, which completely blocks the sun and is often opaque in color, or sunscreen containing additional chemicals that absorb UVA radiation and release it as heat. Both options may involve using a lotion or spray that include an increased number of extra chemicals, which may distress some users even more than the additional rays. The alternative, of course, is to stay inside.

However, the connection between UV exposure and beta-endorphin production may not be bad thing. Fisher himself believes that the endorphins may result from the body’s recognition of the benefits of vitamin D, which are also from the sun. Additionally, endorphins can be triggered by a number of activities that are beneficial to the body, such as exercise. Theoretically, it’s possible to become addicted to anything that produces this happy chemical; runner’s high is a very real sensation also caused by endorphins, and those who become accustomed to a jog every morning may become agitated when they are not able to. Yet to date, there have been no cases of true physical withdraw from a lack of endorphins from exercise or the sun.

Fisher and his colleague’s research may indicate why we continue to engage behaviors we know may harm us; the discovery of the link between melanin production and beta-endorphins could lead scientists to find other activities that lead to the same types of chemical connections. But for now, despite some of the fear-mongering inspired by this latest research it’s probably safe to say that anything, including the sun’s rays, can be enjoyed in moderation.