Ex vivo evaluation of radical sun protection factor in popular sunscreens with antioxidants

Background: UVA induces tissue damage via the production of radical oxygen species. Adding antioxidants to UV filters in sunscreens is a novel photoprotective strategy. The topical application of antioxidants in sunscreen can potentially neutralize the UVA-induced free radicals. Objectives: We sought to assess the degree of free radical protection offered by sunscreens with antioxidants and attempted to differentiate the contribution of free radical protection from that of the UV filters. Method: Twelve sunscreen products were purchased. The degree of UVA protection (UVA-PF) was measured via an in vitro assay according to a European guideline (Colipa). In addition, an electron spin resonance (ESR) spectroscopy-based assay was used to measure the radical skin protection factor (RSF) and antioxidant power (AP) of each product. Results: The sun protection factor (SPF) values of the sunscreens ranged from 15 to 55, and the UVA-PF values ranged from 2.4 to 28.2. The RSF values ranged from 2.4 to 27.1. There is a high correlation between RSF and UVA-PF. The AP values for nearly all the products were 0, and two products (#4 and #9) had very. low AP values of 16 and 12, respectively. Limitations: The study only evaluated a small number of sunscreen products, and only ex vivo and in vitro methods were used to assess the products. Conclusions: The idea of combining UV filters with antioxidants is appealing. Current sunscreen products on the market offer free radical protection, but the majority of the radical protection is from UV filters rather than antioxidants. (J Am Acad Dermatol 2011;65:525-30.)