Sunscreen SPFs: clear as daylight?
Recently issued public health guidance on skin cancer prevention from the National Institute for Health and Clinical Excellence (NICE) recommends that, used properly, a sunscreen with a sun protection factor (SPF) of at least 15 is enough.1 On the face of it, this advice seems reasonable given the theory that sun protection, whether from a sunscreen, a shirt, or shade, need only have an SPF of 15 to prevent sunburn from all-day exposure to tropical sunshine.2 The problem, though, is that a sunscreen only delivers this degree of sun protection if it is applied to the skin at a thickness of 2mg/cm2, the conditions under which manufacturers apply the standard test for SPF. In reality (as we discuss elsewhere in this issue of DTB3), people using sunscreens typically apply much less than this and get no more than half, at best, of the protection indicated by the labelled SPF.
NICE says “SPF 15 is sufficient if applied adequately”. But applying sunscreen “adequately” (i.e. at 2mg/cm2) over a large part of the body is almost impossible, as with this amount, the sunscreen runs off the skin and it is difficult to achieve a cosmetically pleasing application. Using it “adequately” is also costly, since whole-body coverage for a single application for an adult at 2mg/cm2 requires around 35mL of sunscreen. Applying this much at least every 2 hours, as NICE also recommends, would require a standard 200mL bottle of sunscreen every 2–3 days.
In our view, the NICE advice on sunscreen use is not in the interests of public health. Products labelled with an SPF of 30 (together with a 4- or 5-star rating to indicate broad-spectrum ultraviolet screening effect) will more reliably deliver adequate sun protection to most people who use sunscreens and would …
