A recent review by the Cochrane Institute has put some conventional wisdom about sunscreen and skin protection methods—like long sleeves, hats, and shade—into question. Apparently, despite plenty of urgings to use these methods to prevent skin cancer, the actual proof for effectiveness is nowhere near conclusive.
The Cochrane Institute is a non-profit that performs reviews of medical literature in order to collect consistent findings and help promote the use of evidence-based medicine. In this instance, the Institute looked at what the literature had to say about sunscreen and sun protection being able to prevent the most common skin cancers: basal cell carcinoma and cutaneous squamous cell carcinoma. They did not examine effects on the rarer but more dangerous melanoma.
The researchers used fairly basic selection criteria for their review. They would only look at randomly controlled clinical trials which could offer information about the benefits and adverse effects of sun protection methods in adults and children as part of the general population (i.e.: not any high-risk groups). Interestingly, only one study met the criteria: an Australian study that compared daily and occasional use of sunscreen in a general population. The results were negative and the overall strength of the evidence was deemed to be low. No studies were found that looked at sun protection methods such as hats, long sleeves, or seeking shade.
This type of situation is one where science can be unintuitive. There is ample, strong evidence that excess sun exposure and sunburns can increase the risk of skin cancers, and it is definitely known that sunscreen and protective measures will reduce how much UV exposure the skin receives. What is missing here is quality research linking the protections offered by sunscreen, shade, and the like to actual reductions in skin cancers.
The key word here is “quality”. The highest standard for medical evidence is a randomized clinical trial, but there are very real ethical and practical problems with telling one group to actively not protect themselves from a carcinogen you want them to get exposed to.
What the Cochrane review has done, therefore, is highlighted a challenge in performing research, not proven sunscreen and sun protection ineffective. It is possible that another review with different selection criteria might produce different findings on how to reduce skin cancer risk, but for now all the review has done is raised more questions than answers.
Sanchez, G., et. al., “Sun protection for preventing basal cell and squamous cell skin cancers,” Cochrane Database of Systematic Reviews, 2016; 10.1002/14651858.CD011161.pub2.