The sun protection factor (SPF) is commonly used to convey a sunscreen’s effectiveness in protecting against UV radiation that causes sunburn (ie, erythema-inducing radiation [EIR]).1 Importantly, the EIR burden depends on the proportion of EIR actually transmitted through the sunscreen to the skin (% EIR transmitted) and not on the proportion of EIR absorbed by the sunscreen (% EIR absorbed). Doubling SPF from, say, 30 to 60 halves % EIR transmitted from 3.3% to 1.7%, thus doubling protection2 (Figure, A). Unfortunately, however, media and health professionals often incorrectly state that SPFs beyond 30 offer only minor improvements in sun protection, arguing that the increase in % EIR absorbed by the sunscreen is less pronounced than the corresponding increase in SPF values3,4 (eg, 96.7% < 98.3% vs 30 ≪ 60). However, only changes in % EIR transmitted directly relate to changes in SPF; changes in % EIR absorbed do not. In this study, we evaluated whether dermatology experts are able to adequately assess improvements in sunscreen effectiveness based on the following information formats: SPF vs % EIR absorbed vs % EIR transmitted.
Herzog SM, Lim HW, Williams MS, de Maddalena ID, Osterwalder U, Surber C. Sun Protection Factor Communication of Sunscreen EffectivenessA Web-Based Study of Perception of Effectiveness by Dermatologists. JAMA Dermatol. 2017;153(3):348-350. doi:10.1001/jamadermatol.2016.4924