Sun kissed skin is that desirable trait that many people strive for even though it is known that prolonged UV exposure is a risk factor for skin cancer. Skin cancer is the most common form of cancer in the US and over 9,500 people will die from melanoma this year, so why is tanning still so popular? A recent study in mice may help answer this question.
The study, published in Cell shows that mice exposed repeatedly to UV light developed an addiction to the light through the release of β-endorphins. This addiction was characterized by increases in pain thresholds and withdrawal symptoms when endorphin production was inhibited. How do endorphins contribute to addiction? External endorphins like morphine or fentanyl act on the same receptors as β-endorphins and induce a strong sense of euphoria or happiness. Once you have a small amount of the drug, the body requires more and more of it to get the same level of high (called tolerance). In the case of UV light, repeated exposure to the tanning rays causes a similar tolerance and withdrawal as morphine in the mice such that they need to keep tanning to keep feeling the high. A similar type of high is seen in runners and people who exercise and is potentially mediated by endorphins.
One of the questions these results pose is why would something as dangerous as tanning be addictive? There is a biological purpose to sun exposure in the production of vitamin D by UVB rays. It is possible that the release of endorphins and subsequent addiction like symptoms ensured that our ancestors would continue to get UVB exposure and have adequate vitamin D production. However, in the modern era with supplemented vitamin D, this mechanism has now contributed to the rise in tanning behaviours in people and potentially in addiction to tanning seen in young people.
While this study helps answer some questions about how tanning behaviours are so prevalent in our society even though they are detrimental to our health, it should be noted that the work was done on mice and therefore the results need to be validated on humans. Mice are furred and generally nocturnal so could have different mechanisms in place to deal with UV exposure. Having said that, there is plenty of evidence showing potential link between addictive behaviours in people and UV exposure (1, 2, 3). How should the results of this study be interpreted? Sun exposure is necessary for vitamin D production in our body, however, extended periods of sun exposure especially without protection leads to damage to our cells that could translate into cancer and endorphin mediated addiction could explain how this risky behaviour becomes common in our society. People who have problems with excessive tanning may benefit from treatments used for other forms of addiction. Also recent legislation limiting tanning bed exposure in teens is a good first step to helping them live a long healthy life. While a healthy glow might be seen as beautiful, a life full of cancer and chemotherapy is anything but.