Last updated: 6-Jul-2011
Sun & Ultraviolet Radiation
Skin cancer is one of the most common cancers in the world, with the rates increasing in some jurisdictions, e.g., Australia, the US.[1],[2] In particular, there were dramatic increases in the prevalence of malignant melanoma in recent decades. The lifetime risk of developing a malignant melanoma in North America is currently about 1 in 100. This compares with the year 1935, when the rate was 1 in 1,500.[3] The difference may be accounted for by an increase in outdoor leisure activities, though this presumably has been partially offset by more indoor work.[4] Concerns continue over changes in the atmosphere, and especially ozone depletion, which may result in increased ultraviolet (UV) exposure and more skin cancer.[5]
UV radiation is known to damage skin; acute exposure causes sunburn and chronic exposure results in loss of elasticity and increased aging (sometimes called photoaging). Absorption of UV triggers a thickening of the superficial skin layers and an increase in skin pigmentation, which serve to protect the skin against future sunburns. Unfortunately, this protective mechanism, as well as direct DNA damage and immunosuppression, makes the skin more vulnerable to cancer.[6] In particular, strong evidence exists of a dose-response relationship between non-melanoma skin cancer (see below) and cumulative exposure to UV radiation.[7],[8]
It is important to distinguish skin cancers. In addition to malignant melanoma, which accounts for the largest proportion of mortality from skin cancers, there are two other main types, basal cell carcinoma and squamous cell carcinoma. These carcinomas occur frequently but are difficult to track epidemiologically as they are usually treated successfully without requiring hospitalization or a review of a pathologic specimen. Because of the heterogeneity of reporting, the data tables of the Canadian Cancer Statistics reports actually exclude the estimated 76,000 cases of non-melanoma skin cancer.[9]
There is some evidence that skin cancer rates are levelling off and the mortality rate even declining for women in Canada, though still increasing for men.[10] This matches an overall decline in mortality rates for all cancer as reported in the latest Canadian statistics.[11] This does not lessen the need to respond preventively. For example, though the acceleration stopped in the late 1980s in Ontario, reported skin cancer prevalence is still much higher now than in the 1970s.[12] BC’s skin cancer rates also have doubled in 20 years. The province has the highest melanoma prevalence in the country, accounting for 100 annual deaths.[13] This compares with about 700 melanoma-related deaths every year in Canada as a whole.[14]
The story about UV radiation has been complicated in recent years by a number of factors, in addition to the atmospheric ozone changes already noted.
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There are significant health benefits from appropriate doses of UV. Production of vitamin D through such exposure is the most important source of the vitamin for most people in the world. Vitamin D serves many significant functions, and has been shown to have a protective effect against osteoporosis, arthritis, hypertension, diabetes and many types of cancer.[15]
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Some subgroups of melanoma and basal cell carcinoma do not seem to be caused by UV exposure (e.g., some skin cancers have a genetic base).[16]
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The persistent notion that suntans are healthy, or at least healthy-looking.[17]
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The fact of the growing popularity, especially among adolescents and young people, of artificial tanning devices that emit UV radiation.[18],[19],[20] The evidence which shows that such practices increase skin cancer is strongest for the non-malignant forms of the disease.[21] The concerns about these devices have prompted new regulations requiring warning labels describing the UV exposure that they entail.[22]
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The complexities of defining and testing an appropriate measure of sun protective behaviour.[23]
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Serious questions have been asked about the efficacy of one of the most popular and “self-evident” interventions, namely, topical sunscreens. The concern has focused on whether sunscreens afford enough protection against all forms of potentially harmful radiation. Several meta-analyses over the last few years have been unable to confirm any clear relationship between sunscreen use and melanoma incidence. Sunscreens may reduce burning, but, according to some data, actually promote melanoma incidence.[24]
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There is a significant lag time of 10-30 years for the clinical appearance of skin cancer to occur. This can be both a spur to early preventive measures but also an obstacle. The value placed on long-term health protection, especially by children and teens, can be “diminished by the large discount rate assigned to benefits occurring in the distant future.”[25]
There is clearly “room for improvement” when dealing with UV radiation at a population level. For example, an environmental scan conducted in Alberta in 2001 admitted that skin cancer prevention activities were somewhat sporadic and given a much lower priority than other public health issues. In terms of current risky behaviour, results from the US are telling: approximately 32% of adults reported having a sunburn in 2002 and less than a third of adolescents practiced any form of sun protection; the only positive result was the relatively high rate of sunscreen use among children (62%).[26]
[1] Stanton WR, Janda M, Baade PD et al. Primary prevention of skin cancer: a review of sun protection in Australia and internationally Health Promotion International 2004; 19(3): 369-78.
[2] Jemal A, Devesa SS, Hartge P et al. Recent trends in cutaneous melanoma incidence among whites in the United States Journal of the National Cancer Institute 2001; 93(9): 678-83.
[3] BC Cancer Agency. Available at http://www.bccancer.bc.ca/HPI/CME/SkinCancer/CMESkinCancer/ Readings/Prevention/Epidemiology.htm (accessed November 2004).
[4] de Gruijl FR. Skin cancer and solar UV radiation European Journal of Cancer 1999; 35(14): 2003-9.
[5] Yamaguchi N, Kinjo Y, Akiba S et al. Ultraviolet radiation and health: from hazard identification to effective prevention Journal of Epidemiology 1999; 9(6 Suppl): S1-4.
[6] Ichihashi M, Ueda M, Budiyanto A et al. UV-induced skin damage Toxicology 2003; 189(1-2): 21-39.
[7] Suzuki T, Ueda M, Ogata K et al. Doses of solar ultraviolet radiation correlate with skin cancer rates in Japan Kobe Journal of Medical Science 1996; 42(6): 375-88.
[8] Woodhead AD, Setlow RB, Tanaka M. Environmental factors in nonmelanoma skin cancer Journal of Epidemiology 1999; 9(6 Suppl): S102-14.
[9] Canadian Cancer Statistics 2004. Available at http://www.cancer.ca/vgn/images/portal/cit_ 86751114/14/33/195986411niw_stats2004_en.pdf (accessed November 2004).
[10] BC Cancer Agency. Available at http://www.bccancer.bc.ca/HPI/CME/SkinCancer/CMESkinCancer/ Readings/Prevention/Epidemiology.htm (accessed November 2004).
[11] Canadian Cancer Statistics 2004. Available at http://www.cancer.ca/vgn/images/portal/cit_ 86751114/14/33/195986411niw_stats2004_en.pdf (accessed November 2004).
[12] Cancer Care Ontario. Available at http://www.cancercare.on.ca/pdf/CF-May2001-melanoma.pdf (accessed November 2004).
[13] BC Ministry of Health Services, Preventive Health Programs. Available at http://www.healthservices.gov.bc.ca/prevent/sunsmart.html (accessed November 2004).
[14] Canadian Cancer Statistics 2004. Available at http://www.cancer.ca/vgn/images/portal/cit_ 86751114/14/33/195986411niw_stats2004_en.pdf (accessed November 2004).
[15] Grant WB. Health benefits of solar UV-B radiation through the production of vitamin D Photochemical & Photobiological Sciences 2003; 2(12): 1307-8.
[16] Green A, Whiteman D, Frost C et al. Sun exposure, skin cancers and related skin conditions Journal of Epidemiology 1999; 9(6 Suppl): S7-13.
[17] Robinson JK, Rigel DS, Amonette RA. Summertime sun protection used by adults for their children Journal of the American Academy of Dermatology 2000; 42(5 Pt 1): 746-53.
[18] Rhainds M, De Guire L, Claveau J. A population-based survey on the use of artificial tanning devices in the Province of Quebec, Canada Journal of the American Academy of Dermatology 1999;40(4):572-6.
[19] Demko CA, Borawski EA, Debanne SM et al. Use of indoor tanning facilities by white adolescents in the United States Archives of Pediatrics & Adolescent Medicine 2003; 157(9): 854-60.
[20] Cokkinides VE, Weinstock MA, O'Connell MC et al. Use of indoor tanning sunlamps by US youth, ages 11-18 years, and by their parent or guardian caregivers: prevalence and correlates Pediatrics 2002; 109(6): 1124-30.
[21] Karagas MR, Stannard VA, Mott LA et al. Use of tanning devices and risk of basal cell and squamous cell skin cancers Journal of the National Cancer Institute 2002; 94(3): 224-6.
[22] Health Canada, Tanning Lamps. Available at http://www.hc-sc.gc.ca/english/iyh/lifestyles/ tanning.html (accessed November 2004).
[23] Buller DB, Borland R. Skin cancer prevention for children: a critical review Health Education & Behavior 1999; 26(3): 317-43.
[24] Christensen D. Data still cloudy on association between sunscreen use and melanoma risk Journal of the National Cancer Institute 2003; 95(13): 932-3.
[25] Feldman SR, Dempsey JR, Grummer S et al. Implications of a utility model for ultraviolet exposure behavior Journal of the American Academy of Dermatology 2001; 45(5): 718-22.
[26] Saraiya M, Glanz K, Briss P et al. On reducing exposure to ultraviolet light. Preventing skin cancer: findings of the Task Force on Community Preventive Services Morbidity & Mortality Weekly Report. Recommendations & Reports 2003; 52(RR-15):1-12.