Jean-Phillip Okhovat, BS
David Geffen School of Medicine at UCLA
Los Angeles, California
Steven R. Feldman, MD, PhD
Center for Dermatology Research*
Departments of Dermatology, Pathology and Public Health Sciences
Wake Forest School of Medicine
Winston-Salem, North Carolina
People who regularly tan are often more knowledgeable about the dangers of ultraviolet light exposure and the risk of skin cancer than are non-tanners.1 So why do they knowingly keep exposing themselves to a carcinogen? Social influences and so-called “appearance motivation” have been posited as possible reasons, but these are only part of the picture. It turns out that many physical addiction factors may be involved.
To Tan or Not To Tan
In a recent study, researchers investigating the behavioral models that predict sunbathing and indoor tanning2 sampled 589 college females to study the appearance factors related to tanning (sociocultural influences, appearance-related reasons to tan, and appearance-related reasons not to tan) and the perceived threat of skin cancer. In addition, both indoor tanning and sunbathing intentions and behaviors were collected over a six-month time frame. Among the study’s participants, both sociocultural influences (media, family, friends) and appearance-related reasons to tan outweighed the perceived threats of tanning and the appearance-related reasons not to tan.
Biology of Tanning Addiction
Once thought to be a purely behavioral characteristic, tanning may have biological effects that lead some patients to continue exposing themselves to ultraviolet light. In a seminal survey study by Warthan and colleagues, UV light (UVL) tanning was investigated as a type of substance-related disorder (SRD);3 145 beachgoers in Galveston Island, Texas,were evaluated to assess their dependence on UVL tanning, based on two models used to identify SRDs. The researchers employed modified versions of both the standard CAGE questionnaire (normally used for alcoholism screening) and the American Psychiatric Association’s DSM-IV-TR, which includes seven criteria for diagnosing SRDs. Of the 145 participants, 26 percent met the modified CAGE criteria and 53 percent met the modified DMSIV- TR criteria for a substance-related disorder (p=0.03).
A similar study conducted by Harrington, et al.4 also sought to determine the presence of addictive behaviors in participants who frequented indoor tanning salons. As in the Warthan study, the 100 participants completed both a modified CAGE questionnaire and a modified DSM-IV questionnaire. Forty-one percent of the subjects met the criteria for a “tanning addictive disorder.” These studies provided a new paradigm for understanding why people seek out exposure to UV light. The authors suggested that recognizing tanning as a potential SRD might alter future strategies to decrease or eliminate this addictive behavior.
Natural Narcotic Effects
In keeping with this survey research, in vitro and in vivo studies provided a biologic foundation for the addictive properties of tanning. Wintzen and colleagues,5 conducting in vitro studies designed to assess how UV light induces pigmentation, found that UV light exposure induces keratinocytes to synthesize alpha-melanocyte stimulating hormone (α-MSH), a polypeptide derived from the larger protein proopiomelanocortin (POMC).Yet another polypeptide hormone contained within POMC, β-endorphin, was released in addition to the α-MSH. β-endorphin, which binds to narcotic receptors, is the “feel-good” molecule in the body. The possibility that endorphin production underlies tanning behavior provided an exciting new basis for explaining why tanners frequently seek both outdoor and indoor tanning sites, despite knowing the harmful effects (Figure 1).
A 2004 in vivo study by Feldman et al. investigated whether UV exposure can have physiologically reinforcing effects separate from appearance motivation that may contribute to tanning behavior.6The researchers enrolled frequent tanners, identified as those tanning three times a week or more. Subjects tanned in two tanning beds designed to appear the same, except that one emitted UV light and the other did not. Both tanning beds transmitted visible light and appeared identical; however, tanning beds include acrylic sheets that people lie on, and one of the tanning beds had acrylic filters that blocked UV, while the other had no such filters. This allowed for controlled, blinded UV administration. The tanners had sessions in both beds on Mondays and Wednesdays and were then allowed to choose one of the two beds on Fridays. The Monday, Wednesday, and Friday sessions were repeated for six weeks. There were 41 Friday “choice” sessions total, and in 39 of those sessions (95 percent), tanners chose the UV bed; only twice did anyone choose the non-UV bed. Study participants reported a more relaxed mood after UV exposure than after non-UV exposure. This study provided strong confirmation of a biologic mechanism that at least partly drives tanning behavior in frequent tanners. [Figure 2.]
To test whether endorphin production underlies this drive, expanding on an earlier preliminary study, Kaur et al. subsequently conducted a study to determine whether opioid antagonism would block the potential reinforcing effect of indoor tanning in eight frequent tanners and eight infrequent tanner control subjects.7In the earlier study (2005), Kaur and colleagues had given three frequent tanners 50 mg of naltrexone, a narcotic antagonist that effectively blocks central and peripheral opioid receptors.8Two of the subjects developed unexpected nausea, vomiting, and disorientation – symptoms similar to those seen in cases of opioid withdrawal.
In Kaur et al.’s larger study, done the next year, the eight frequent and eight infrequent tanners were given escalating doses of naltrexone. At each dose level, subjects were randomized to receive either naltrexone or placebo, then switched to the other at the next visit. Drug screening was done to assure that the subjects were not taking exogenous narcotics. All eight infrequent tanners completed the trial without adverse events (nausea and/or jitteriness). In contrast, two frequent tanners discontinued the study due to adverse events at a dose of 15 mg naltrexone, and two others also experienced adverse events at 15 mg naltrexone but remained in the study. In the placebo and 5 mg dose of naltrexone conditions, frequent tanners preferred the UV stimulus; but at naltrexone doses of 15 and 25 mg, frequent tanners showed a reduced preference for UV exposure.
Thus, the earlier in vitro studies and confirmatory in vivo human trials provided strong evidence to support the theory that the reinforcing effects of UV exposure may be at least partly mediated by opioids, such as β-endorphin. As opposed to the previous prevailing notion that frequent tanners tan purely for appearance-related motivations, frequent tanning behavior appears to have, at least in part, a physiologic basis.
The Role of the Central Nervous System
Further advances in elucidating the addictive properties of tanning are coming from brain imaging studies designed to assess whether tanning has an effect on the central nervous system (CNS). The brain’s “reward pathway” contains three important structures: the ventral tegmental area (VTA), the nucleus accumbens, and the prefrontal cortex. The VTA is connected to both the nucleus accumbens and the prefrontal cortex via this pathway. [Figure 3.] When activated by a rewarding stimulus, the neurons of the VTA release dopamine into the nucleus accumbens and the prefrontal cortex.
Researchers have sought to investigate the effects of UV radiation (UVR) on the central nervous system by assessing the effects of commercially available tanning on regional cerebral blood flow (rCBF) — a measure of brain activity — using single-photon emission computed tomography (SPECT).9 In a study by Harrington et al., seven frequent tanners were placed under UVA/UVB tanning light during two sessions, one session involving UVR exposure and the other employing filtered UVR. During the unfiltered UVR sessions only, the participants showed a relative increase in rCBF of the dorsal striatum, anterior insula, and medial orbitofrontal cortex, brain regions associated with reward. The blood flow changes were also associated with a temporary decrease in the subjects’ desire to tan. This study added to our understanding of tanning behavior by demonstrating that exposure to UVR has an effect on the CNS reward system,which reinforces tanning behavior in frequent tanners. With this finding, the idea that frequent tanners are tanning solely because of a desire to look darker is no longer tenable.
In the past several years, a wave of research has helped to delineate the complex internal and external (physiologic, psychological, and biochemical) reasons for tanning behavior and tanning addiction. As we improve our understanding of why people continue to engage in an activity that is potentially so harmful, this knowledge may allow investigators to develop better interventions to reduce or even eliminate habitual tanning.
- Mawn VB, Fleischer AB Jr. A survey of attitudes, beliefs, and behavior regarding tanning bed use, sunbathing, and sunscreen use. J Am Acad Dermatol 1993 Dec; 29(6):959-62.
- Cafri G, Thompson JK, Jacobsen PB, Hillhouse J. Investigating the role of appearance-based factors in predicting sunbathing and tanning salon use. J Behav Med 2009 Dec; 32(6):532-44.
- Warthan MM, Uchida T, Wagner RF Jr. UV light tanning as a type of substance-related disorder. Arch Dermatol 2005 Aug; 141(8):963-6.
- Harrington CR, Beswick TC, Leitenberger J, et al. Addictive-like behaviours to ultraviolet light among frequent indoor tanners. Clin Exp Dermatol 2011 Jan; 36(1):33-8.
- Wintzen M, Yaar M, Burbach JP, Gilchrest BA. Proopiomelanocortin gene product regulation in keratinocytes. J Invest Dermatol 1996 Apr; 106(4):673-8.
- Feldman SR, Liguori A, Kucenic M, et al. Ultraviolet exposure is a reinforcing stimulus in frequent indoor tanners. J Am Acad Dermatol 2004 Jul; 51(1):45-51.
- Kaur M, Liguori A, Lang W, et al. Induction of withdrawal-like symptoms in a small randomized, controlled trial of opioid blockade in frequent tanners. J Am Acad Dermatol 2006 Apr; 54(4):709-11.
- Kaur M, Liguori A, Fleischer AB Jr, Feldman SR. Side effects of naltrexone observed in frequent tanners: could frequent tanners have ultravioletinduced high opioid levels? J Am Acad Dermatol 2005 May; 52(5):916.
- Harrington CR, Beswick TC, Graves M, et al. Activation of the mesostriatal reward pathway with exposure to ultraviolet radiation (UVR) vs. sham UVR in frequent tanners: a pilot study. Addict Biol 2012 May; 17(3):680-6.