A proposal for simplifying the labelling of sunscreens

Determination of sun protection factors (SPFs) using the 'gold standard' in vivo method (ISO 24444) is known to be associated with appreciable uncertainty because of experimental variability. Consequently, several in vitro methods have been evaluated, that show promising accuracy, reproducibility and correlation with the in vivo ISO 24444 method. As a way of eliminating the uncertainties associated with both in vivo and in vitro methods, a proposal is made here to dispense with the concept of the SPF and instead to introduce a binary system for labelling the protection afforded by topical sunscreens. Phototesting can be either in vivo or in vitro, with in vivo phototesting requiring only a single area of sunscreen-protected skin to be irradiated. Alternatively, a validated in vitro method could be employed to determine the threshold protection required for assigning products to the appropriate binary category.