Thursday, July 1, 2010

Does Sunscreen Prevent Skin Cancer?

As we turn to summer, cookouts, and more time in the sun, a burning question is whether sunscreen prevents skin cancer. Much media attention has focused on the slow progress made by the FDA to bring US regulations into line with other countries to gain up to date benefits of sunscreen formulation and consumer labeling (see story).  Sun exposure is the major cause of skin cancer, and sunscreen can help protect against sunburn, but can sunscreen prevent skin cancer? Put simply: is sunscreen an effective way to lower the risk of skin cancer?
With more than one million Americans diagnosed each year, skin cancer is not something to be taken lightly. Although it is not usually life threatening, even the least dangerous types of skin cancer require treatment and can be severely disfiguring. At its worst, skin cancer can be deadly, and the most dangerous form, malignant melanoma, will claim over 8,500 lives this year. The rate of this cancer is rising across all sectors of our population increasing the need for prevention strategies for this cancer. Clearly, there is a need for prevention, but it remains uncertain whether sunscreen will meet that need.
Several lines of evidence suggest that sunscreen may play a protective role with respect to skin cancer. The strongest available evidence that sunscreen use is an effective approach to prevention of skin cancer comes from a 4.5-year community-based randomized controlled trial among 1,621 adult residents of a subtropical Australian town. In comparison with people randomized to using sunscreen at their discretion if at all, people randomized to daily use of a broad-spectrum SPF15+ sunscreen showed a 40% reduction in squamous cell carcinoma tumors at the conclusion of the trial [1].
Despite this supportive evidence, epidemiologic results on sunscreen and skin cancer have been mixed. Some studies have suggested that sunscreen may protect against skin cancer, while others have shown just the opposite—that it can increase risk. Non-randomized or observational studies of sunscreen use and skin cancer are plagued by confounding: the driving forces behind sunscreen use also are directly related to skin cancer. For example, susceptibility to sunburn and high sun exposure cannot be separated.  A growing concern is that advice to use sunscreen may lead to longer sun exposure once “protection” is applied, undermining the benefit of sunscreen.
Given the current body of evidence on sunscreen and skin cancer, the International Agency for Research on Cancer [2] has recommended daily use of sunscreen with a sun protection factor (SPF) of 15 or higher for people who work outdoors or who enjoy regular outdoor recreation. However, sunscreen should not be used as the sole method of sun protection nor as a means for extending the amount of time spent in the sun. The best way for individuals to lower their risk of skin cancer is to reduce their sun exposure by combining all strategies:
  • Staying out of the sun between the peak burning hours of 10 a.m. and 4 p.m.;
  • Seeking shade or bringing it (for example, a beach umbrella or tent); and
  • Wearing hats and other protective clothing, like long-sleeve t-shirts and lightweight pants.



Does this approach work? The Centers for Disease Control Task Force on Community Preventive Services  concluded that school-based educational/policy interventions (for children) and recreational-based educational/policy interventions (for adults) are effective in reducing sun exposure [3]. Both types of interventions are well represented by the Australian SunSmart program, ongoing since 1982, (formerly Slip! Slop! Slap!) which aims at reducing UV exposure through access to shade and consistent use of protective clothing, hats, sunglasses, and sunscreen.  Examples of SunSmart programming include accreditation of schools that adhere to its policy and practice requirements and collaboration with governmental agencies to protect outdoor workers.  The program has changed attitudes regarding sun tanning, led to increases in protective behavior, decreased costs of sun protection gear, societal acceptance of more protective attire (including hats, sunglasses, and “neck to knee” swimsuits for children) and, most importantly, decreasing incidence rates of skin cancer [4]. Within Australia, that sun-protective behavior increased from 1987-2002 during which time the SunSmart program was active [5]. The evidence from Australia indicates that active prevention efforts including television advertising campaigns can be highly effective in improving the population wide sun-protective behaviours, resulting in falling age-specific incidence rates for melanoma, in younger birth cohorts [6].   

Building comprehensive approaches to reducing sun exposure, not just using sunscreen, is necessary to achieve our goals of reducing the burden of skin cancer. It is not too late to cover up when in the sun and enjoy the outdoors this summer.
  

Literature cited
1.            Green, A., et al., Daily sunscreen application and betacarotene supplementation in prevention of basal-cell and squamous-cell carcinomas of the skin: a randomised controlled trial. Lancet, 1999. 354(9180): p. 723-9.
2.            The International Agency for Research on Cancer Working Group on the Evaluation of Cancer-Preventive Agents, Sunscreens, in IARC Handbooks of Cancer Prevention. 2001, International Agency for Research on Cancer: Lyon, France.
3.            Saraiya, M., et al., Preventing skin cancer: findings of the Task Force on Community Preventive Services On reducing Exposure to Ultraviolet Light. MMWR Recomm Rep, 2003. 52(RR-15): p. 1-12.
4.            Montague, M., R. Borland, and C. Sinclair, Slip! Slop! Slap! and SunSmart, 1980-2000: Skin cancer control and 20 years of population-based campaigning. Health Educ Behav, 2001. 28(3): p. 290-305.
5.            Dobbinson, S.J., et al., Weekend sun protection and sunburn in Australia trends (1987-2002) and association with SunSmart television advertising. Am J Prev Med, 2008. 34(2): p. 94-101.
6.            Hill, D. and R. Marks, Health promotion programs for melanoma prevention: screw or spring? Arch Dermatol, 2008. 144(4): p. 538-40.


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