Natural Antioxidants as Sunscreen SPF Boosters: Mechanisms, Benefits and Challenges

Prolonged exposure to ultraviolet (UV) rays is a major extrinsic factor causing sunburn, oxidative stress, inflammation, photoaging, and carcinogenesis of the skin. Although traditional sunscreen materials have been shown to provide a powerful protective effect against UV-induced damage to the skin, there is still a need to address the shortcomings of such sunscreen materials, which are: the photo-instability of the absorbing materials, skin irritation, environmental impacts, and inadequate protection against long-wavelength UVA rays. These limitations have created a growing interest in natural antioxidants as supplementary sunscreen materials. Natural antioxidants successfully demonstrated considerable potential to reinforce their photoprotective efficacy through different mechanisms. These antioxidants neutralize the free oxygen produced due to the effects of UV radiation, help in stabilizing the chemical antioxidants against photodegradation, reduce erythema and inflammation, and show their ability to reinforce the barrier function. Along with improving their biological protection, antioxidant supplementation possesses the ability to show enhanced sunscreen efficacy without increasing the amount of conventional chemical filters. The review critically addresses the mechanisms by which natural antioxidants can be effective in the improvement of the efficacy of sunscreens, as well as the significant benefits, along with the formulation-related challenges, limitations in regulations, recent experimental evidence, and prospects.