Effectiveness of different substrate materials for in vitro sunscreen tests

Abstract

In vitro measurements of sunscreen products are used to assess their reliability in terms of photoprotection and photo-stability. In this study, several substrates have been fully characterized for in vitro sunscreen testing. The following different substrates have been utilised in the study: roughened PMMA plates, Transpore, Vitro-Skin, roughened quartz plate and a laboratory prepared roughened PTFE plate. The suitability of these substrates for SPF evaluation has been investigated by performing total absorbance measurements of seven sunscreen products with different SPF values produced by the same manufacturer. Application of sunscreen products on Transpore, roughened quartz plate, PMMA, PTFE and Vitro-Skin was performed efficiently. With regard to photo-stability of the substrate materials, only PMMA plate, PTFE and roughened quartz plate showed to be photo-stable after UV irradiation. With regard to SPF tests, our results indicate that Transpore, roughened quartz plate and Vitro-Skin are preferable to assess SPF values because of a better correlation between in vitro and in vivo measurements. Our study also confirms that an initial calibration must be performed for sunscreen products labelled with different SPF values. Finally, the results of our measurements demonstrate that, although a correlation between in vitro and in vivo SPF results can be established, it is never exactly 1:1.