Cutaneous delivery of natural antioxidants: the enhancement approaches

Topically applied natural antioxidants can be an effective treatment for inhibiting oxidative damage and photoaging of the skin. Due to the barrier function of the stratum corneum (SC), it is necessary to use an enhancement approach to promote the cutaneous absorption of natural antioxidants. Some factors that should be considered when developing delivery systems for natural antioxidants include increased solubility, enhanced storage stability, improved permeability and bioavailability, skin targeting, and minimal side effects. This review describes the skin delivery systems for natural antioxidant permeation that have been developed during the last decade. The antioxidants introduced include vitamins, polyphenols, and carotenoids. Various types of formulations are employed to improve the skin penetration of the antioxidants, such as hydrogels, cyclodextrin, microemulsions, nanoparticles, liposomes and niosomes. This review focuses on the introduction of natural antioxidants used in skin protection, the mechanisms of antioxidant activity on the skin, and formulation designs for enhancing absorption and efficacy.