A new in vitro test method to assess the UVA protection performance of sun care products

UVA protection provided by sunscreens is an issue of major importance due to increasing knowledge about UVA-induced skin damage. In Europe there is no officially accepted method to determine the level of UVA protection. The objective of the present study was to develop a new method combining the merits of an in vitro model, which is simple and reproducible, with the required information of in vivo efficacy. For the in-vitro part of the method transmission measurements were carried out through thin layers of product sample on roughened PMMA-plates (Plexiglas®). The amount of sunscreen was adjusted to the roughness of the plates to ensure an optimal distribution of the sample and measurement in the optimal range of the spectrophotometer. Mathematical normalisation of the absorption spectrum to the label (in vivo) SPF makes it possible to predict the level of in vivo UVA protection. Furthermore, this new method shows a very good correlation with in vivo results for the UVA protection performance (PPD) of 45 different commercial sunscreens. A method is described that is suitable for predicting the UVA protection delivered by sunscreens, which should be considered in any future official discussion on UVA methodology.