The impact of UV-filter combination on the number of free radicals generated in sunscreen formulations and the skin following UV-VIS irradiation was assessed via electron spin resonance spectroscopy using a spin-probing approach. Four UV-filter combinations that differed in their photostability and range of UVA absorbance coverage were investigated. Fewer free radicals
were generated in the sunscreen formulation when a photostable UVA filter system was used, compared to a stabilized UVA filter system. Additionally, fewer free radicals were generated in the skin when a sunscreen with long UVA protection extending to the short visible range was used, compared to a sunscreen with minimal UVA protection. This study showed that the photostability
of a UV-filter system is central to the generation of free radicals in a formulation, and that long UVA-blue light protection is key for avoiding the generation of free radicals in the skin. A sunscreen product exhibiting both photostable UVA protection and long UVA-blue light protection is therefore the most appropriate choice for protecting against ROS-induced skin damage.