20 Recent meta-analyses have not supported the findings of these RCTs, finding no significant effectiveness of sunscreen for preventing either melanoma or nonmelanoma skin cancers. In organ transplant recipients, a population at high risk of morbidity and death from skin cancer, a prospective single-centre study of 120 matched patients showed that the use of sun protection factor (SPF) 50 sunscreen over 24 months reduced the development of actinic keratoses, squamous cell carcinomas and, to a lesser extent, basal cell carcinomas. 12 Another large Australian RCT showed a significantly reduced rate of development of actinic keratoses (a precursor to squamous cell carcinoma) among participants randomized to regular use of sunscreen, compared with controls who used a nonactive base cream over 1 summer season (rate ratio 0.62, 95% CI 0.54 to −0.71). 5 A predefined subgroup analysis in this trial confirmed that regular use of sunscreen over a 4.5-year period can arrest signs of skin aging caused by photodamage. 18 Almost 15 years after the completion of the study, participants who used sunscreen daily throughout the 4.5-year study period showed a significantly reduced risk of invasive melanoma (hazard ratio 0.27, 95% CI 0.08 to −0.97), although very few invasive melanomas were noted, given the long lead time for this type of tumour. 4, 18 However, the incidence of basal cell carcinomas was not significantly reduced, possibly owing to the protracted pathogenesis of basal cell carcinomas. 16, 17 A well-conducted community-based 4.5-year RCT of 1621 adult Australians, with follow-up for more than a decade, found a 40% lower incidence of squamous cell carcinomas among participants randomized to recommended daily sunscreen compared with participants assigned to use sunscreen on a discretionary basis (rate ratio 0.61, 95% confidence interval 0.46 to 0.81). 11 – 15 Despite the challenges of studying skin cancer, owing to its multifactorial pathogenesis and long lead time, the following evidence supports the use of sunscreen in the prevention of skin cancer.Įxperimental studies from the 1980s and 1990s showed that sunscreens protect against cell damage consistent with carcinogenesis in animal models. What is the effectiveness of sunscreens in preventing photoaging and skin cancer?Įvidence from observational studies, 11 a large randomized controlled trial (RCT) 12 and smaller, nonrandomized experimental studies 13 – 15 support the effectiveness of sunscreens in preventing the signs of photoaging, including wrinkles, telangiectasia and pigmentary alterations induced by ultraviolet radiation. (2-Hydroxy-4-methoxyphenyl)(2-hydroxyphenyl) methanone Terephthalylidene dicamphor sulfonic acidĢ-Ethoxyethyl 3-(4-methoxyphenyl) propenoate We summarize evidence related to the effectiveness and harms of sunscreen to help physicians counsel their patients ( Box 1).Ģ-Ethylhexyl 2-cyano-3,3-diphenylacrylate 6, 7 Yet, since the development of the first commercial sunscreen in 1928, questions regarding the safety and efficacy of sunscreen have been raised, and more recently, the impact of sunscreens on the environment has become a cause for concern. 4, 5 Both the Canadian Dermatology Association and the American Academy of Dermatology recommend the use of sunscreen for the prevention of skin cancer. 1 Because exposure to ultraviolet radiation is estimated to be associated with 80%–90% of skin cancers, the use of sunscreen - which blocks ultraviolet radiation - is promoted as an important means of preventing skin cancers, 2, 3 as well as sunburn and skin photoaging (see definitions in Appendix 1, available at Use of sunscreen has been shown to reduce the incidence of both melanoma and nonmelanoma skin cancers. In Canada, more than 80 000 cases of skin cancer are diagnosed every year. Ultraviolet filters found within chemical sunscreens may be harmful to the environment.
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