Indoor tanning is a popular practice, particularly by adolescent and young women, that results in high levels of ultraviolet (UV) A and B exposure.1 UVA and UVB are both known to induce DNA damage, specifically C to T point mutations. Though many patients believe that sunburn is associated with skin damage, DNA mutations have been shown to occur even before sunburn develops. In addition, a popular reason that individuals use indoor tanning is to create a “base tan” that prevents sunburn or reduces their risk of skin cancer with outdoor sun exposure. However, a population-based case-control study demonstrated that indoor tanning neither prevents subsequent sunburn nor confers protection against skin cancer, and it increases the risk of melanoma regardless of whether individuals develop a sunburn as a result of outdoor sun exposure.2
In 2009, the World Health Organization’s International Agency for Research on Cancer Working Group (IARC) classified UV-emitting tanning devices as carcinogenic to humans based on evidence from its meta-analysis.3 In 2014, the U.S. Food and Drug Administration (FDA) reclassified sunlamps, or UV-emitting tanning devices, from class 1 to class 2 (special controls) devices, and instituted special measures to ensure reasonable assurance of safety.4 With this ruling, the FDA required that sunlamps display a visible black box warning that the product should not be used by individuals younger than age 18, and that the warning include information about contraindications in any consumer instructions or consumer-directed catalogs, specification sheets, descriptive brochures, and web pages.5
Though it seems well understood that indoor tanning is associated with skin cancer, the data are somewhat mixed and are based on primarily poor-quality epidemiologic studies.
Several meta-analyses of epidemiologic studies suggest an association between indoor tanning and an increased risk of melanoma. The IARC meta-analysis conducted in 2006 included 19 case-control, cohort, or cross-sectional studies and found that “ever use” significantly increased the risk of melanoma compared with “never use” (summary relative risk [SRR], 1.15; 95% CI, 1.00-1.31), but did not find a dose-response relationship.6 However, most of the individual studies included in the analysis found no significant association. Another meta-analysis published in 2012 included 27 studies primarily from Europe (but also some from the United States and Australia) and found a significant association between ever use of indoor tanning beds and melanoma risk compared with never use (SRR, 1.20; 95% CI, 1.08-1.34).7 This analysis showed a dose-response of a 1.8% increase in melanoma risk for each year of tanning bed use. In addition, patients who initiated indoor tanning prior to age 35 demonstrated a greater risk of developing melanoma (SRR, 1.87; 95% CI, 1.41-2.48).
A meta-analysis published in 2014 included 31 studies with 14,956 cases and 233,106 controls and similarly demonstrated that indoor tanning bed use was significantly associated with an increased risk of melanoma (odds ratio [OR], 1.16; 95% CI, 1.05-1.28), including studies that enrolled patients from 2000 onward (OR, 1.22; 95% CI, 1.03-1.45).8 Though the authors of these meta-analyses concluded that indoor tanning increases the risk of melanoma, authors of a more recent meta-analysis disagree.
This meta-analysis was published in 2018 and included 31 case-control and cohort studies with 11,706 cases and 93,236 controls, which the authors deemed contained poor-quality data, similar to the findings of the prior meta-analyses.9 Ever use of indoor tanning beds was significantly associated with melanoma compared with never use (OR, 1.19; 95% CI, 1.04-1.35) and in studies conducted in the United States (OR, 1.32; 95% CI, 1.05-1.66) and Australia (OR, 1.30; 95% CI, 1.00-1.69), but not in Europe (OR, 1.10; 95% CI, 0.95-1.27) or among studies at low risk of bias (OR, 1.15; 95% CI, 0.94-1.41). The authors concluded that these data do not support the hypothesis of a causal link between indoor tanning and melanoma due to the moderate association demonstrated by studies of poor quality, such as lack of adjusting for potential confounders and recall bias.
A cohort study published in 2017 that was not included in the 2018 meta-analysis included 141,045 women from the Norwegian Women and Cancer Study, who were recruited between 1991 and 2012 and had a mean follow-up of 13.7 years.10 Ever use of indoor tanning was significantly associated with melanoma compared with never users (RR, 1.24; 95% CI, 1.05-1.46); similarly, current use increased the risk of melanoma compared with noncurrent use (RR, 1.27; 95% CI, 1.10-1.47). Though the risk was present regardless of age of initiation, women who began indoor tanning prior to age 30 were at a greater risk of developing melanoma compared with never users (RR, 1.34; 95% CI, 1.05-1.66). This study also found a dose-response, with melanoma risk increasing with higher numbers of indoor tanning sessions. Indoor tanning also lowered the age of melanoma diagnosis. Melanoma was diagnosed a mean of 2.2 years earlier among women who started indoor tanning prior to 30 years of age and 1.2 years earlier among women who began indoor tanning at 30 years or older compared with never users.