Background The ability of sunscreen products to delay sun-induced skin erythema is indicated by the sun protection factor (SPF), which is measured using an internationally agreed sunscreen thickness of 2 mg cm−2.
Objectives To determine the thickness of sunscreen used under practical conditions.
Methods In two double-blind randomized trials performed in five different places in Europe in 1997 and 1998, 148 18–24-year-old students received either an SPF 10 or an SPF 30 sunscreen to be used during their summer holidays.
Results Complete, detailed data on quantities of sunscreen used and skin areas on to which sunscreen was applied were available for 124 students. The median thickness of sunscreen applied was 0·39 mg cm−2. We found no variation in sunscreen thickness according to sex, skin phototype, study place or SPF.
Conclusions Our results indicate that most consumers do not benefit from the SPF indicated on sunscreen bottles, and do not support the idea that thickness of sunscreen applied would be greater if these products were cheaper. We suggest that information on ability of a sunscreen product to prevent sunburn should be adapted in order to reflect actual usage patterns.