UV Addiction: A Form of Opiate Dependency

In the August issue of the Archives, Keen et al¹ discuss recent clinical evidence that UV-seeking behavior should perhaps be seen as an addictive disorder.^{2 - 3} This insight is important because it implies that excessive tanning behavior should be approached as a form of substance abuse and that altering patients' sunning habits will not be a trivial matter. Unfortunately, Keen et al do not mention recent molecular and clinical data supporting the idea that excessive UV tanning behavior results from an addiction to endogenous opioids.^{4 - 5} I believe that these recent data strongly justify treating excessive sun-seeking behavior as an addiction. This idea has important implications for dermatologic practice, and the recent report describing its possible molecular background⁴ may have escaped most readers' attention.

Induction of pigmentation by UV irradiation requires keratinocytes to secrete α-melanocyte-stimulating hormone (α-MSH), a cleavage product of the prohormone peptide pro-opiomelanocortin (POMC). In 2007, Cui et al⁴ elegantly demonstrated that the tumor suppressor protein p53, which is stabilized on detection of DNA damage, induces POMC production in keratinocytes. Besides α-MSH, POMC cleavage yields β-endorphin, an endogenous opioid that can induce, among other effects, analgesia and euphoria. This fascinating mechanism might have evolved to provide analgesia for sunburns related to accidental overexposure to UV radiation, but one might equally and perhaps more plausibly interpret it as a reward system that makes the organism seek sun exposure to, for example, ensure adequate vitamin D production. One might wonder what has selected for DNA damage, rather than some form of light or UV sensing, as a trigger for pigmentation.

Regardless, in our present society, with sun exposure so easy to come by, the mechanism may no longer be adaptive. In my view, it can certainly help to explain why sunning can be addictive. Naloxone has been shown to induce withdrawal symptoms in regular sunbathers.⁵ This observation further supports the notion that endogenous opioids are involved in tanning behavior.

In conclusion, recent molecular biological findings lend support to the idea that excessive sunbathing should be seen as an addiction. These findings also suggest that excessive sunbathers should be treated as addicts and that simple advice from a physician to avoid excessive sun exposure will probably not alter their behavior.

Corresponding Author: Dr Van Steensel, Department of Dermatology, Maastricht University Medical Center, PO Box 5800, 6202 AZ Maastricht, the Netherlands (m.vansteensel@mumc.nl).

Financial Disclosure: None reported.