Evaluation of sunscreen products using a reconstructed skin model exposed to simulated daily ultraviolet radiation: relevance of filtration profile and SPF value for daily photoprotection

Background: The recent definition of a standard daily ultraviolet radiation (DUVR) has allowed us to reproduce non-zenithal sun exposure conditions. Exposure to simulated DUVR induces biological damage in human skin, suggesting the need for an appropriate photoprotection. Methods: Sunscreen products were evaluated using human reconstructed skin in vitro. Two commercial sunscreens (A and B) having similar sun (burn) protection factor (SPF) values (∼15) but different profiles of transmission over the UVA range were tested on skin models exposed to increasing doses of DUVR. Another pair of sunscreens was also tested. One (product C) had an SPF ∼18 with a well-balanced UVB–UVA profile and the other (product D) an SPF of ∼27 with low UVA absorption. Biological parameters were assessed by (i) histology, (ii) vimentin immunostaining for dermal fibroblasts, and (iii) analysis of matrix metalloprotease (MMP)-1 secretion. Results: Products A and C gave better protection from DUVR with regard to fibroblast alterations and MMP-1 release compared with products B and D, respectively. Conclusion: To ensure an efficient daily photoprotection from DUVR, the filtration profile of the product should be well balanced with a sufficient level of UVA absorption. With regard to end points evaluated in this study, our data suggest that a higher SPF value does not compensate for low UVA filtration.