This extensive article reviews much of the experimental and epidemiological evidence around the use of sunscreen to prevent skin cancer over the last two decades. The author discusses many aspects of ultraviolet radiation (UVR) exposure and mechanisms of skin damage and sunscreen properties in detail including:
- mechanisms of UVR interaction with human skin and the pathways for which DNA damage occurs and skin cancers including basal cell carcinoma, squamous cell carcinoma and melanoma develop,
- specific properties of different categories of sunscreen as defined by their active ingredients (e.g. physical barriers such as zinc oxide and chemical absorbers such as oxybenzone) and how they work to block solar UVR from damaging skin,
- the spectral range of UVR that sunscreens are effective and the length of time before re-application is necessary.
The author also discusses potential direct adverse health effects from use of the sunscreens by reviewing results on risks of penetration of active ingredients into the bloodstream. Further, comment is provided about environmental and aquatic ecosystem risk concerns from pollution caused when sunscreen ingredients wash off during outdoor recreational activities, resulting in decisions to ban sunscreens containing oxybenzone by various jurisdictions in the US.
The author then moves on to discuss the level of evidence supporting skin cancer risks from solar UVR exposure and the net effect that sunscreen has had on reducing those risks. The author concludes that the protective effects of sunscreen use, although supported in many studies, are yet to be clearly demonstrated due to conflicting conclusions within the total body of scientific and health evidence. Further, more work is required to assess sustained efficacy to block UVR based on the photostability of the active ingredients in sunscreens and any potential direct health impacts on humans and the environment.
Photochemical & Photobiological Sciences
Commentary by ARPANSA:
This article presents extensive information on solar UVR health effects, types of sunscreens and how they work in blocking UVR. Contextual review of scientific and health research related to the use of sunscreen in preventing skin cancer is also provided. Although the author asserts that there is no clear evidence that sunscreen use has had a definitive effect on reducing the incidence of skin cancer, particularly melanoma, a number of studies have reported a protective effect with sunscreen use. For example, in 2011 Green et al reported that a follow up from a randomised trial conducted on a cohort of residents in Queensland demonstrated a reduced melanoma rate in participants that applied sunscreen on a daily basis. Another Australian study published in 2018 by Watts et al reported that application of sunscreen in early childhood significantly reduced melanoma in adults.
The discussion given on the effectiveness of particular sunscreens along with potential health effects and environmental damage highlights the importance of clinical trials and other hazard assessments. However, the article demonstrated that there are many types of sunscreen on the market giving regulators and consumers options and alternatives for managing any negative health or environmental impacts. Further, discussions on the other sun protection strategies including wearing hats, protective clothing, sunglasses and seeking shade highlight that sunscreen should not be relied upon as a single strategy for skin cancer prevention. As many studies have reported a decrease in skin cancer risk through sunscreen use, ARPANSA and Cancer Council Australia still advise its application as part of the five sun protection measures, Slip Slop Slap Seek and Slide.