Measurement of UVA protection

Although the importance of the UVA protection of sunscreens in preventing sun-induced damage to the skin is becoming increasingly apparent, there are currently no officially recognized methods to measure the UVA protection performance of sunscreens. The new in vitro method described in this article allows a prediction of the result of an in vivo measurement that is valid for all types of sunscreen products. Forty-five commercially available sunscreens were studied using roughened polymethylmethacrylate plates (PMMA) as the substrate. The in vitro UVA protection was determined using the UVA spectrum of the sunscreen after this had been fitted mathematically to meet the measured in vivo SPF. To show the validity of this method the results were correlated with an endpoint in the UVA range determined in vivo. This work demonstrates that a very good prediction of the in vivo results is obtained. No dependence on the emulsion base, filter composition or photostability of the products was observed. Fitting the UVA spectrum to the measured in vivo SPF eliminates the need for pre-irradiation of the products. It could be shown that this new in vitro method to measure UVA protection performance is applicable to and valid for all sunscreens available on the market.