Skin Cancer, Melanoma, and Exposure to Ultraviolet Light

What is UV light and how does it relate to sunlight?

"Terrestrial life is dependent on radiant energy from the sun." [IARC Monographs - 100D]


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"The carcinogenic effect of natural sunlight is possibly related primarily to ultraviolet B (UVB) in the 290-320 nm band." [Rosenstock, p. 815]

What are the main types of skin cancer?

"The most invasive form of skin cancer, melanoma, has a high mortality rate, particularly when not detected early. Non-melanoma skin cancers (NMSCs), such as basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) are more common but less likely to metastasize, with only a small proportion leading to mortality. . . . There may be a link between risk of developing melanoma and outdoor work although the evidence is less clear." [Horsham 2014]

"Prognosis varies depending on the type of skin cancer being treated:

  1. Basal cell carcinoma: generally excellent with conventional treatment.
  2. Squamous cell carcinoma: excellent for small lesions removed early and completely.
  3. Malignant melanoma: 5-year survival is almost 100% for very superficial lesions removed early. However, thick lesions and melanoma that has spread to other organs have poor prognosis." [Skin Cancer - University of Maryland Medical Center]

What is melanoma?

"Melanoma" usually refers to an in situ or invasive cancer of melanocytes, which may also be called "malignant melanoma". although the term "benign melanoma' is occasionally used clinically to refer to very slowly growing, pigmented intraocular tumors, it is not in current use in the medical literature. . . . In addition to serving as markers of increased risk, nevi are direct precursors of melanoma in some fraction of cases. However, it is important to recognize that nevi are observed in 1% of infants and are observed in virtually all adults. Thus the malignant potential of common acquired nevi is minuscule. . . . Sun exposure is the main cause of melanoma. From differences in its incidence between usually and rarely exposed body skin and between white-skinned and black-skinned people living in the same environment, it has been estimated that over 90% of melanomas are due to sun exposure in mainly European-origin populations living in areas of high ambient solar UV radiation. . . . The consistently very low rates of melanoma in people of Asian origin are puzzling because many Asians, particularly East Asians have comparatively light skin." [Schottenfeld, p. 1196]

"Childhood is believed to be a susceptible window for long-term harmful effects of UV, as evidenced by clear differences in skin cancer risk between child and adult migrants from high to low latitudes. . . . Cutaneous melanoma is rare in children and adolescents with only 2–3% of all cases observed in patients under age 20 years. . . . More recently, however, melanoma survival in Swedish children and adolescents has been reported to be as high as 90% (1993–2002). . . . In the only available case–control study of melanoma in childhood neither acute nor chronic exposure to solar UV radiation was associated with increased melanoma, suggesting that, since most Queensland children experience high levels of sun exposure in early life, there was insufficient variability in any of the markers of UV exposure to discriminate the small number of cases from controls. The findings also suggest that genetic factors play a relatively greater role in very early childhood melanoma rather than sun exposure. The case–control study of melanoma in adolescence showed a slightly higher proportion of cases than controls reporting more than 10 episodes of peeling sunburns, and there was a statistically significant trend to increasing risk of melanoma with increasing numbers of peeling or blistering sunburns." [Green 2011]

Does occupational exposure to the sun increase your risk for melanoma?

"Intermittent’ sun exposure, which loosely equated with certain sun-intensive activities, such as sunbathing, outdoor recreations, and holidays in sunny climates, generally showed moderate-to-strong positive associations with melanoma. However, ‘chronic’ or ‘more continuous’ exposure, which generally equated with ‘occupational’ exposure, and total sun exposure (sum of ‘intermittent’+‘chronic’), generally showed weak, null or negative associations." [IARC Monographs - 100D]

"Although the development of some types of melanoma shows a certain dependence on UV exposure, there is insufficient data on occupational exposure so that at this time melanomas are not under consideration as tumors induced by occupational UV exposure." [Fartasch 2012]

"We present up to 45 years of cancer incidence data by occupational category for the Nordic populations. The study covers the 15 million people aged 30-64 years in the 1960, 1970, 1980/1981 and/or 1990 censuses in Denmark, Finland, Iceland, Norway and Sweden, and the 2.8 million incident cancer cases diagnosed in these people in a follow-up until about 2005. . . . Sunburns in early ages in susceptible people are accepted as the major cause of malignant melanoma. . . . In the present study, fishermen and forestry workers ranked as the groups with the lowest risk of malignant melanoma in men. This may well be explained by the fact that these groups have constant sun exposure and are not burnt in the sun, as opposed to leisure time sun exposure which is often followed by sunburns." [Pukkala 2009]

"Outdoor work was associated with a 10% excess of squamous- and basal-cell carcinoma and a 9% excess of melanomas of the head, face and neck, but a 22% deficit of melanomas of other sites. Office work was associated with a 31% excess of melanomas of other sites, and about average rates of squamous and basal cell carcinomas and of melanomas of the head, face and neck. . . . The worldwide increase in melanoma incidence noted in the last 30 years is largely the result of an increase in lesions of the trunk and limbs. There has been relatively little increase in melanomas of the head, face and neck. Since office workers experience high rates specifically of melanomas of the unexposed parts of the body, they should hold important clues to the recent increase in melanoma incidence." [Beral 1981]

"Sun exposure has been accepted as the main cause of cutaneous melanoma in humans by reputable groups such as the International Association for Research on Cancer (1992). However, the evidence often is described as weak or conflicting. . . . To date, 35 published case-control studies have reported results on this topic. We present an overview of these studies. . . . In contrast, the overall result for occupational exposure shows a small, though significant, reduction in risk. Occupational exposure in general should be easier to document than intermittent exposure, so this provides strong evidence against there being a clear increase in risk at maximum levels of occupational exposure. . . . Thus, these results are consistent with the intermittent exposure hypothesis, that cutaneous melanoma is increased primarily by intermittent unaccustomed sun exposure. It seems likely that the neutral or protective effect of heavy chronic exposure is related to protective mechanisms such as tanning and skin thickening, but this may not be the total explanation. . . . The associations with intermittent exposure and sunburn give scientific justification for programmes to reduce individual sun exposure, by concentrating on the reduction of intermittent unaccustomed exposure." [Elwood 1997]

"The association between sun exposure and the risk of melanoma seems complex. Previous studies have shown that although sunburn and intermittent sun exposure are associated with increased risk of melanoma, there is no, or an inverse, association between occupational (more continuous pattern) sun exposure and melanoma risk. . . .  Our results suggest that occupational sun exposure does not increase risk of melanoma, even of melanomas situated on the head and neck. This finding seemed not to be due to negative confounding of occupational sun exposure by weekend sun. . . . There may be other explanations for the observed null or inverse associations of occupational sun exposure with melanoma. Melanin has a role in absorbing ultraviolet radiation, is an antioxidant and scavenges free radicals. More continuous sun exposure increases melanin production and epidermal thickness and thus may confer protection against melanoma through photoadaptation." [Vuong 2013]

"We performed a pooled analysis of 15 case–control studies (5700 melanoma cases and 7216 controls), correlating patterns of sun exposure, sunburn and solar keratoses (three studies) with melanoma risk. . . .  Recreational sun exposure and sunburn are strong predictors of melanoma at all latitudes, whereas measures of occupational and total sun exposure appear to predict melanoma predominately at low latitudes. . . . Sun exposure has been identified in epidemiological studies as the leading environmental cause of melanoma, but the lack of a simple dose–response relationship between total sun exposure and risk of melanoma has been perplexing. In general, studies have reported a positive association for recreational (intermittent) sun exposure and an inverse association with occupational (more continuous) exposure. . . . Overall, increased total sun exposure was not associated with melanoma risk at any site in the high latitudes or with melanoma on the trunk and head and neck at any latitudes (Table 4). It was, however, associated with melanoma on the limbs and, more weakly, the head and neck, at low latitudes: the fully adjusted pORs were 1.5 (95% CI: 1.0–2.2) and 1.3 (95% CI: 0.8–2.2). . . . Sunburn before the age of 15 was a consistently significant risk factor for all three latitude regions. . . . Self-selection against outdoor work by fair-skinned people living at low latitudes, which we have demonstrated, could also lower the estimates of melanoma risk in those who had high occupational exposure. . . . Recreational sun exposure and sunburns are strong predictors of melanoma on less frequently sun-exposed body sites, at all latitudes." [Chang 2009]

"Constitutional factors and sun exposure were examined among 256 cases of melanoma and 273 controls in three counties of western Washington State. . . . Sun exposure in adulthood and occupational sun exposure were not related to melanoma risk." [White 1994]

"A systematic revision of the literature was conducted in order to undertake a comprehensive meta-analysis of all published observational studies on melanoma. . . . Following a systematic literature search, relative risks (RRs) for sun exposure were extracted from 57 studies published before September 2002. Intermittent sun exposure and sunburn history were shown to play considerable roles as risk factors for melanoma, whereas a high occupational sun exposure seemed to be inversely associated to melanoma." [Gandini 2005]

"Epidemiological studies have confirmed the hypothesis that the majority of all melanoma cases are caused, at least in part, by excessive exposure to sunlight. In contrast to squamous cell carcinoma, melanoma risk seems not to be associated with cumulative, but intermittent exposure to sunlight." [Leiter 2008]

Does exposure to artificial UV light increase your risk for melanoma?

"Based on 19 informative studies, ever-use of sunbeds was positively associated with melanoma (summary relative risk, 1.15; 95% CI, 1.00–1.31), although there was no consistent evidence of a dose–response relationship. . . . The association with ever-use of such equipment, or use more than 15–20 years prior to diagnosis of melanoma, was weak, and evidence regarding a dose–response relationship was scant." [IARC 2007a]

"Concerning use of sunbeds and/or sunlamps and risk of melanoma results so far have been somewhat inconclusive. . . . Thus, the case group comprised 674 eligible persons. . . . A total of 584 cases (86%) and 1028 controls (76%) answered the questionnaire. . . . Among 571 cases (females, 50.3%; males, 49.7%) and 913 controls (females, 50.8%; males, 49.2%), 250 cases (44%) and 372 controls (41%) reported ever using sunbeds. . . . The OR for developing malignant melanoma after ever having used sunbeds was 1.2 (95% CI 0.9–1.6), adjusted for history of sunburn after age 19 years, hair colour, skin type and number of raised naevi. . . . A particular concern in case-control studies is recall bias (i.e. if cases report differently than controls), since it can distort associations in an unpredictable manner. . . . Nevertheless, it can not be solely ruled out that awareness of the diagnosis of malignant melanoma and the hypothesis of an association between sunbed use and melanoma occurrence may have perverted the answers to the questions on sunbed use." [Westerdahl 2000]

Does exposure to UV light have beneficial effects?

"Excessive sun exposure at all ages is discouraged largely because of the increased risk of melanoma and other skin cancers. However, further research is needed to define the amount of solar or artificial UV exposure that might be beneficial. Longer follow-up and additional prospective studies with comprehensive assessment of UV exposure and vitamin D measurement are warranted." [Yang 2011]

"The mortality rate amongst avoiders of sun exposure was approximately twofold higher compared with the highest sun exposure group, resulting in excess mortality with a population attributable risk of 3%. . . . The results of this study provide observational evidence that avoiding sun exposure is a risk factor for all-cause mortality. Following sun exposure advice that is very restrictive in countries with low solar intensity might in fact be harmful to women’s health." [Lindqvist 2014]

"Doctors are learning that vitamin D has many health benefits. It may even help to lower the risk for some cancers. Vitamin D is made naturally by your skin when you are in the sun. How much vitamin D you make depends on many things, including how old you are, how dark your skin is, and how strong the sunlight is where you live." [Amercan Cancer Society]

"The recommendation for the avoidance of all sun exposure has put the world's  population at risk of vitamin D deficiency." [Holick 2008]

"The aim of this study was to assess whether patients with skin cancer have an altered risk of developing other cancers. The study cohort consisted of 416,134 cases of skin cancer and 3,776,501 cases of non-skin cancer as a first cancer extracted from 13 cancer registries. . . . Sunburn, in particular, and skin type are risk factors for melanoma. . . . We hypothesise that skin cancer patients have a higher mean sun exposure and a higher vitamin D serum level than the average population, and therefore they should have decreased risk of the vitamin D insufficiency-related cancers listed above. This effect should be stronger in countries with high solar exposure. To elucidate this hypothesis, we studied the joint occurrence of skin cancers and other primary cancers in a cohort extracted from 13 cancer registries. . . . In sunny countries, the risk of second primary cancer after non-melanoma skin cancers was lower for most of the cancers except for lip, mouth and non-Hodgkin lymphoma. Conclusions: Vitamin D production in the skin seems to decrease the risk of several solid cancers (especially stomach, colorectal, liver and gallbladder, pancreas, lung, female breast, prostate, bladder and kidney cancers). The apparently protective effect of sun exposure against second primary cancer is more pronounced after non-melanoma skin cancers than melanoma, which is consistent with earlier reports that non-melanoma skin cancers reflect cumulative sun exposure, whereas melanoma is more related to sunburn." [Tuohimaa 2007]

"A population-based cohort study of 29 508 women who answered a questionnaire in 1990–92, of whom 24 098 responded to a follow-up enquiry in 2000–02. They were followed for an average of 15.5 years. RESULTS: Among the 17 822 postmenopausal women included, 166 cases of endometrial cancer were diagnosed. We used a multivariate Cox regression analysis adjusting for age and other selected demographic variables to determine the risk of endometrial cancer. Women using sun beds >3 times per year reduced their hazard risk (HR) by 40% (0.6, 95% confidence interval (CI) 0.4–0.9) or by 50% when adjusting for body mass index or physical activity (HR 0.5, 95% CI 0.3–0.9), and those women who were sunbathing during summer reduced their risk by 20% (HR 0.8 95% CI 0.5–1.5) compared with women who did not expose themselves to the sun or to artificial sun (i.e., sun beds). CONCLUSION: Exposure to artificial sun by the use of sun beds >3 times per year was associated with a 40% reduction in the risk of endometrial cancer, probably by improving the vitamin D levels during winter." [Epstein 2009]

"Sun exposure is the single most important risk factor for skin cancer, but sun exposure may also have beneficial effects on health. . . . We examined the entire Danish population above age 40 years from 1980 through 2006, comprising 4.4 million individuals. . . . In this nationwide study, having a diagnosis of skin cancer was associated with less myocardial infarction, less hip fracture in those below age 90 years and less death from any cause. . . . Median surveillance time was 23 years. . . . As skin cancer is a marker of a substantial sun exposure, these results indirectly suggest that sun exposure might have beneficial effects on health.  An association between high levels of vitamin D and lower cardiovascular morbidity and mortality has been reported in several epidemiological studies, whereas randomized controlled trials show no effect of supplementation with vitamin D on risk of cardiovascular mortality." [Brondum-Jacobsen 2013]

"This was a cohort study comprising 40,000 women (1000 per year of age from 25 to 64 years) who were drawn from the southern Swedish population registry for 1990 and followed for a mean of 11 years. . . . Swedish women who sunbathed during the summer, on winter vacations, or when abroad, or used a tanning bed, were at 30% lower risk of VTE than those who did not. . . . Women with more active sun exposure habits were at a significantly lower risk of VTE. We speculate that greater ultraviolet B light exposure improves a person's vitamin D status, which in turn enhances anticoagulant properties and enhances the cytokine profile." [Lindqvist 2009]

"An inverse relationship exists between vitamin D levels and diabetes mellitus. However, little is known about the correlation of sun exposure habits and type 2 diabetes mellitus (DM). . . . A South Swedish cohort study comprising 1000 women from each age group between 25 and 64 (n=40,000) drawn from the Southern Swedish population registry 1990-1992. At the inception of the study 74% answered the inquiry (n=29,518) and provided detailed information on their sun exposure habits and other variables. A follow-up inquiry was sent 2000-2002 which 24,098 women answered. The mean follow-up time was 11 years. . . . Our findings indicated that women with active sun exposure habits were at a 30% lower risk of having DM, as compared to those with non-active habits. . . . The study supports that sunlight is involved in the glucose metabolism." [Lindqvist 2010]

"Essential features of the epidemiology and photobiology of cutaneous malignant melanoma (CMM) in Norway were studied in comparison with data from countries at lower latitudes. Arguments for and against a relationship between ultraviolet radiation (UV) from sun and artificial light and CMM are discussed. Our data indicate that UV is a carcinogen for CMM and that intermittent exposures are notably melanomagenic. This hypothesis was supported both by latitude gradients, by time trends and by changing patterns of tumor density on different body localizations. However, even though UV radiation generates CMM, it may also have a protective action and/or an action that improves prognosis." [Moan 2014]

"However, some evidence suggests that total sun exposure in childhood is associated with an increased risk for melanoma and occupational sun exposure may be associated with a decreased risk for melanoma. . . . Based on five fair-quality studies, sunscreen use has no clear protective or harmful effect on the risk for melanoma, although the case-control studies examining this risk have major limitations. . . . . In a cohort of women living at high latitudes (n=2,016), however, those who avoided direct sun exposure were at risk for vitamin D deficiency during the winter and spring months. . . . Regular sunscreen use can prevent squamous cell carcinoma, but it is unclear if it can prevent basal cell carcinoma or melanoma." [Lin 2011]

How can you prevent melanoma?

"Current evidence is inadequate to determine whether these measures reduce incidence or mortality of melanoma; in nonmelanoma skin cancers (basal cell and squamous cell carcinoma), sun protection does decrease the incidence of new cancers." [Merck Manual, p. 749]

"If cumulative sun exposure does not affect melanoma risk at countries at higher latitudes, such as the United States, and if chronic, low-grade exposure to sunlight is protective against CMM in these countries, then perhaps our emphasis on counseling patients in the United States should focus on sunburn, not sunlight, avoidance." [Planta 2011]


Revised: May 30, 2018

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