In vitro approaches to evaluation of Sun Protection Factor

The efficacy of sunscreen products has been recognized as an important public health issue. Adequate methods for assessment of the level of protection should be developed and standardised. While the SPF COLIPA testing method in vivo has been used for years, preference should be given to in vitro testing methods as in vivo methods raise ethical concern. The present study aims to assess possible in vitro approaches based on diffuse transmission spectroscopy, published previously by Diffey, and two methods based on measurements of UVB transmission through a defined layer of a sunscreen product applied on various UV-transparent substrates. The attenuated UVB intensity, using different UV light sources, is detected radiometrically and transformed to real SPF value by means of a calibration curve, which is based on an extensive number of measurements performed using both in vivo and in vitro method The outcome of the three in vitro methods employed in the study showed great differences in the obtained SPF values in comparison with reference SPF determined by means of the COLIPA method in vivo. The high variability of in vitro results suggests that main attention should be focused on substrate selection simulating the human skin surface and homogenous product application. The in vitro screening methods may represent a fast and reasonable tool reducing the number of in vivo experiments and risks related to UV exposure of human subjects, when the technical test parameters are adjusted and optimized.