Science Exposed—What Should the Minimum Recommended SPF Be to Avoid Sunburn?
By: Brian Diffey, PhD DSc, Newcastle University, UK
Posted: January 26, 2012, from the February 2012 issue of Cosmetics & Toiletries.
Editor’s note: “Science Exposed” is a new column in Cosmetics & Toiletries featuring guest authors. It complements our well-known technical and formulating-focused content by digging into industry controversies to strip them down to the scientific facts. The content presented here is intended to provoke constructive debate within the industry to lead toward an eventual resolution. Here, sun protection expert Brian Diffey, PhD DSc, critiques the current SPF test method and urges the industry to make necessary changes. Readers are invited to engage in this debate on C&T magazine’s LinkedIn Group (join us, if you are not yet a member) or to submit their comments or suggestions for other topics to CTEdit@allured.com.
In January 2011, the National Institute for Health and Clinical Excellence (NICE) in the United Kingdom issued public health guidance on skin cancer prevention and recommended that sunscreens possessing a Sun Protection Factor (SPF) of at least 15 were sufficient if applied adequately.1 More recently, in June 2011, the US Food and Drug Administration (FDA) published its long-awaited monograph2 in which the agency gave similar advice: …We continue to direct consumers to follow a comprehensive sun protection program that includes use of sunscreens with broad-spectrum SPF values of 15 or higher.
This advice is intended to focus on the minimum level of protection considered necessary to claim that sunscreens, when combined with limiting time in the sun and wearing clothes to protect sun-exposed areas, reduce the risk of skin cancer and early skin aging.2 However, a major reason that people use sunscreens, especially during recreational exposure, is to avoid sunburn. So is an SPF 15 sunscreen sufficient to achieve this goal?
It is certainly true that a photo-protective device, whether a sunscreen, shirt or shade, need only possess a protection factor of 15 to prevent sunburn in consumers behaving typically during all-day exposure to tropical summer sunshine.3 So in that sense, a sunscreen with an SPF 15 would be sufficient if it were delivering fifteenfold protection, which it would if it were applied at 2 mg/cm2—the thickness chosen by manufacturers to facilitate the testing process. But this amount is not based on user studies of how sunscreen is applied in real life.
It is well-known that people generally apply much less than this amount, and so will actually be getting less protection—typically, protection equivalent to about one-third of the labeled SPF.4 This mismatch between expected and delivered photoprotection has led many commentators into the trap of believing that consumers use inadequate amounts of sunscreen for protection, when the reality is the reverse: People use the quantity they feel comfortable with and in this sense are using the “correct” amount. It is the labeled SPFs that are misleading.