High‐energy visible light at ambient doses and intensities induces oxidative stress of skin—Protective effects of the antioxidant and Nrf2 inducer Licochalcone A in vitro and in vivo

Background Solar radiation causes skin damage through the generation of reactive oxygen species (ROS). While UV filters effectively reduce UV‐induced ROS, they cannot prevent VIS‐induced (400‐760 nm) oxidative stress. Therefore, potent antioxidants are needed as additives to sunscreen products. Methods We investigated VIS‐induced ROS formation and the photoprotective effects of the Nrf2 inducer Licochalcone A (LicA). Results Visible spectrum of 400‐500 nm dose‐dependently induced ROS in cultured human fibroblasts at doses equivalent to 1 hour of sunshine on a sunny summer day (150 J/cm2). A pretreatment for 24 hours with 1 µmol/L LicA reduced ROS formation to the level of unirradiated cells while UV filters alone were ineffective, even at SPF50+. In vivo, topical treatment with a LicA‐containing SPF50 + formulation significantly prevented the depletion of intradermal carotenoids by VIS irradiation while SPF50 + control did not protect. Conclusion LicA may be a useful additive antioxidant for sunscreens.