The role of ultraviolet (UV) exposure in melanoma genesis is often misunderstood. The two most important mechanisms by which UV exposure increases the risk of melanoma are induction of DNA damage, often after sunburning, primarily due to wavelengths from 290 to 325 nm (the erythema region) and oxidative damage caused by free radicals generated during UVA exposure.
Both mechanisms can act on melanocytes as well as on immune cells in the skin and in that way decrease the efficiency of immuno-effects on premalignant melanocytes.
Wearing sunscreen, which blocks erythemal radiation well, but UVA less well, will influence the melanoma risk associated with UV exposure. Sunscreen use seems to reduce the risk of melanoma for latitudes below about 40 degrees (near the latitude for Manhattan and Salt Lake City) but to increase the risk at higher latitudes6.
In addition to vitamin D production, chronic UV exposure also causes elastosis (breakdown of elastic tissue or collagen). For reasons not fully understood, melanomas develop less well in skin with elastosis. For example, melanoma in Sweden develops on the face and hands from around the age of 55 years, but from around the age of 35 years on the trunk and legs8. The difference seems to be due to whether the skin is chronically exposed as from occupation or sporadically exposed as from trips to the beach. Smoking also causes elastosis or skin wrinkling, and smokers have reduced risk of melanoma910. Further discussion on the role of sun exposure on different body sites is given by Caini11.
A study in Connecticut found increased survival for persons with evidence of large sun exposure:
Sunburn, high intermittent sun exposure, and solar elastosis were statistically significantly inversely associated with death from melanoma. Melanoma thickness, mitoses, ulceration, and anatomic location on the head and neck were statistically significantly positively associated with melanoma death. In a multivariable competing risk analysis, skin awareness (with versus without, HR = 0.5, 95% CI = 0.3 to 0.9, P = .022) and solar elastosis (present versus absent, HR = 0.4, 95% CI = 0.2 to 0.8, P = .009) were strongly and independently associated with melanoma death after adjusting for Breslow thickness, mitotic index, and head and neck location, which were also independently associated with death12.
A group in Italy has conducted a number of meta-analyses of risk factors for melanoma. Meta-analyses are quantitative reviews of studies on a particular topic. Among the findings were:
- A high number of nevi (moles) is a significant risk factor13
- 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 melanoma14
- Phenotypic factors such as pale skin, freckles, blue eye color, and red or blond hair color are associated with increased risk of melanoma15
- The melanocortin-1-receptor (MC1R), one of the major genes that determine skin pigmentation, has many variants. Those associated with red hair and fair skin were significantly correlated with melanoma risk in a manner suggesting a role in melanoma development via pigmentary and non-pigmentary pathways16
A study in Germany found that outdoor activities in childhood were protective against melanoma, although sunburn in childhood was a risk factor17. A study of cancer mortality rates in Spain using mortality rates for nonmelanoma skin cancer as an index of solar UVB exposure, found melanoma mortality rate inversely correlated with this index for females but uncorrelated for males18. Those who have signs of chronic sun exposure, such as farmers and other outdoor workers, are not very likely to get melanoma in general19.
A case-control study in England found “Overall the clearest relationship between reported sun exposure and risk was for average weekend sun exposure in warmer months, which was protective (OR 0.67, 95% CI 0.50-0.89 for highest versus lowest tertile of exposure)”20.
A study from Australia, which has the fairest-skinned people living in region of very high solar UV doses found in general there was little significant correlation between amount of sun exposure and risk of melanoma. However, rates were increased by a factor of two-t0-three for those diagnosed with melanoma prior to age 29 years who had more than 10,000 hours of sun exposure21. As the average mortality rate for melanoma is 1 per 100,000 inhabitants per year aged 23-33 years [WHO mortality database], implying an incidence rate of 5-10 per 100,000 inhabitants per year, this does not imply a large absolute risk. Breast cancer mortality rates for women of that age range are somewhat higher.
There is evidence from ecological studies that UVA is a risk factor for melanoma. For those with northern European ancestry, melanoma rates decrease with increasing latitude with a gradient that is much lower than for either squamous cell carcinoma or basal cell carcinoma45. UVB is an important risk factor for the two non-melanoma skin cancers, and UVB doses change more with latitude than do UVA doses.
Uveal and vulvar melanoma are also vitamin D sensitive24. Under conditions of increasing rates of melanoma on exposed skin, related to latitude or to time, the rates of vulval and uveal melanomas decrease.
People are often advised to avoid the sun or to use sunscreens when in the sun. This advice does not necessarily lead to reduced risk of melanoma6, while it certainly reduces production of vitamin D.
It was estimated that if all Americans raised their serum 25(OH)D levels to over 40 ng/mL from 16 ng/mL for Black Americans, 21 ng/mL for Hispanic Americans, and 26 ng/mL for White Americans27, mortality rates might be reduced by 400,000 deaths/year while melanoma death rates might rise from 9000/year to 18,00028.
Page last edited: 18 July 2011
- Garland, C. F. Garland, F. C. Gorham, E. D. Rising trends in melanoma. An hypothesis concerning sunscreen effectiveness. Ann Epidemiol. 1993 Jan; 3 (1): 103-10.
- Garland, C. F. Garland, F. C. Gorham, E. D. Epidemiologic evidence for different roles of ultraviolet A and B radiation in melanoma mortality rates. Ann Epidemiol. 2003 Jul; 13 (6): 395-404.
- Godar, D. E. Landry, R. J. Lucas, A. D. Increased UVA exposures and decreased cutaneous Vitamin D(3) levels may be responsible for the increasing incidence of melanoma. Med Hypotheses. 2009 Apr; 72 (4): 434-43.
- Moan, J. Dahlback, A. Setlow, R. B. Epidemiological support for an hypothesis for melanoma induction indicating a role for UVA radiation. Photochem Photobiol. 1999 Aug; 70 (2): 243-7.
- Moan, J. Porojnicu, A. C. Dahlback, A. Ultraviolet radiation and malignant melanoma. Adv Exp Med Biol. 2008; 624104-16.
- Gorham, E. D. Mohr, S. B. Garland, C. F. Chaplin, G. Garland, F. C. Do sunscreens increase risk of melanoma in populations residing at higher latitudes?. Ann Epidemiol. 2007 Dec; 17 (12): 956-63.
- Dennis, L. K. et al. Sunburns and risk of cutaneous melanoma: does age matter? A comprehensive meta-analysis. Ann Epidemiol. 2008 Aug; 18 (8): 614-27.
- Dal, H. et al. Does relative melanoma distribution by body site 1960-2004 reflect changes in intermittent exposure and intentional tanning in the Swedish population?. Eur J Dermatol. 2007 Sep; 17 (5): 428-34.
- Grant, W. B. Skin aging from ultraviolet irradiance and smoking reduces risk of melanoma: epidemiological evidence. Anticancer Res. 2008 Nov-Dec; 28 (6B): 4003-8.
- Delancey, J. O. Hannan, L. M. Gapstur, S. M. Thun, M. J. Cigarette smoking and the risk of incident and fatal melanoma in a large prospective cohort study. Cancer causes & control : CCC. 2011 Jun; 22 (6): 937-42.
- Caini, S. Gandini, S. Sera, F. Raimondi, S. Fargnoli, M. C. Boniol, M. Armstrong, B. K. Meta-analysis of risk factors for cutaneous melanoma according to anatomical site and clinico-pathological variant. European journal of cancer. 2009 Nov; 45 (17): 3054-63.
- Berwick, M. Armstrong, B. K. Ben-Porat, L. Fine, J. Kricker, A. Eberle, C. Barnhill, R. Sun exposure and mortality from melanoma. J Natl Cancer Inst. 2005 Feb 2; 97 (3): 195-9.
- Gandini, S. Sera, F. Cattaruzza, M. S. Pasquini, P. Abeni, D. Boyle, P. Melchi, C. F. Meta-analysis of risk factors for cutaneous melanoma: I. Common and atypical naevi. Eur J Cancer. 2005 Jan; 41 (1): 28-44.
- Gandini, S. Sera, F. Cattaruzza, M. S. Pasquini, P. Picconi, O. Boyle, P. Melchi, C. F. Meta-analysis of risk factors for cutaneous melanoma: II. Sun exposure. Eur J Cancer. 2005 Jan; 41 (1): 45-60.
- Gandini, S. Sera, F. Cattaruzza, M. S. Pasquini, P. Zanetti, R. Masini, C. Boyle, P. Melchi, C. F. Meta-analysis of risk factors for cutaneous melanoma: III. Family history, actinic damage and phenotypic factors. Eur J Cancer. 2005 Sep; 41 (14): 2040-59.
- Raimondi, S. Sera, F. Gandini, S. Iodice, S. Caini, S. Maisonneuve, P. Fargnoli, M. C. MC1R variants, melanoma and red hair color phenotype: a meta-analysis. Int J Cancer. 2008 Jun 15; 122 (12): 2753-60.
- Kaskel, P. Sander, S. Kron, M. Kind, P. Peter, R. U. Krahn, G. Outdoor activities in childhood: a protective factor for cutaneous melanoma? Results of a case-control study in 271 matched pairs. Br J Dermatol. 2001 Oct; 145 (4): 602-9.
- Grant, W. B. An ecologic study of cancer mortality rates in Spain with respect to indices of solar UVB irradiance and smoking. Int J Cancer. 2007 Mar 1; 120 (5): 1123-8.
- Chang, Y. M. Barrett, J. H. Bishop, D. T. Armstrong, B. K. Bataille, V. Bergman, W. Berwick, M. Bracci, P. M. Elwood, J. M. Ernstoff, M. S. Gallagher, R. P. Green, A. C. Gruis, N. A. Holly, E. A. Ingvar, C. Kanetsky, P. A. Karagas, M. R. Lee, T. K. Le Marchand, L. Mackie, R. M. Olsson, H. Osterlind, A. Rebbeck, T. R. Sasieni, P. Siskind, V. Swerdlow, A. J. Titus-Ernstoff, L. Zens, M. S. Newton-Bishop, J. A. Sun exposure and melanoma risk at different latitudes: a pooled analysis of 5700 cases and 7216 controls. Int J Epidemiol. 2009 Jun; 38 (3): 814-30.
- Newton-Bishop, J. A. Chang, Y. M. Elliott, F. Chan, M. Leake, S. Karpavicius, B. Haynes, S. Fitzgibbon, E. Kukalizch, K. Randerson-Moor, J. Elder, D. E. Bishop, D. T. Barrett, J. H. Relationship between sun exposure and melanoma risk for tumours in different body sites in a large case-control study in a temperate climate. European journal of cancer. 2011 Mar; 47 (5): 732-41.
- Cust, A. E. Jenkins, M. A. Goumas, C. Armstrong, B. K. Schmid, H. Aitken, J. F. Giles, G. G. Kefford, R. F. Hopper, J. L. Mann, G. J. Early-life sun exposure and risk of melanoma before age 40 years. Cancer causes & control : CCC. 2011 Jun; 22 (6): 885-97.
- Mouret, S. Baudouin, C. Charveron, M. Favier, A. Cadet, J. Douki, T. Cyclobutane pyrimidine dimers are predominant DNA lesions in whole human skin exposed to UVA radiation. Proc Natl Acad Sci U S A. 2006 Sep 12; 103 (37): 13765-70.
- Moan, J. et al. Uveal and cutaneous malignant melanoma and solar radiation. Time trends and dependence on latitude. Dermato-Endocrinology. 2010 Jan; 2 (1): 2-8.
- Moan, J. Porojnicu, A. C. Dahlback, A. Grant, W. B. Juzeniene, A. Where the sun does not shine: is sunshine protective against melanoma of the vulva?. J Photochem Photobiol B. 2010 Nov 3; 101 (2): 179-83.
- Rass, K. Reichrath, J. UV damage and DNA repair in malignant melanoma and nonmelanoma skin cancer. Adv Exp Med Biol. 2008; 624162-78.
- Smit, N. P. Vink, A. A. Kolb, R. M. Steenwinkel, M. J. van den Berg, P. T. van Nieuwpoort, F. Roza, L. Pavel, S. Melanin offers protection against induction of cyclobutane pyrimidine dimers and 6-4 photoproducts by UVB in cultured human melanocytes. Photochem Photobiol. 2001 Sep; 74 (3): 424-30.
- Ginde, A. A. Liu, M. C. Camargo, C. A., Jr. Demographic differences and trends of vitamin D insufficiency in the US population, 1988-2004. Arch Intern Med. 2009 Mar 23; 169 (6): 626-32.
- Grant, W. B. In defense of the sun: An estimate of changes in mortality rates in the United States if mean serum 25-hydroxyvitamin D levels were raised to 45 ng/mL by solar ultraviolet-B irradiance. Dermatoendocrinol. 2009 Jul; 1 (4): 207-14.