Photostability of commercial sunscreens upon sunlight exposure

Abstract

Introduction: The use of sunscreens is recommended to reduce skin damage and prevent skin cancer. However, evidence has shown that sunscreen can undergo degradation processes induced by ultraviolet (UV) radiation which can lead to reduction or loss of photoprotective capacity, generation of free radicals and toxic intermediates which react with skin structures generating biological damage. Objective: To evaluate the photostability of four sunscreen formulations with Sun Protection Factor (SPF) 30 added by different chemical and physical UV filters. Material and Methods: Each product was exposed to solar radiation from 10 a.m. to 15 p.m. (UV index: 6.0). The areas under the curves (AUC) of the absorbance spectrum of the formulations before and after radiation exposure were used to calculate the ratio between the AUC before and after the solar radiation (AUCI). Results: Only two formulations, which presented the AUCI higher than 0.8, were considered photostable. Despite having the same SPF 30, formulations showed different absorption spectrum in regions of UVA1, UVA2 and UVB and the photostability of the products tested varied considerably. Conclusion: The development of photostable formulations is critical because degradation products of UV filters can act as photo-oxidants. Furthermore, increased exposure to UV radiation due to the reduction of the photoprotective capacity of unstable products increases the risk of burns and skin cancer.