Photoprotection of natural flavonoids

Overexposure to ultraviolet (UV) radiation can cause a number of skin disorders such as erythema, edema, hyperpigmentation, immunosuppression, photoaging, and skin cancer. Since the level of UV radiation is increasing as a result of depletion of the stratospheric ozone and climate change, the protection of human skin against the harmful effects of UV radiation is an urgent need. Topical application of sunscreens is a strategy to protect the deleterious effect of UV radiation on the skin. Sunscreens today contain one or several synthetic UV filter molecules which protect the UV radiation exposed on the epidermis. These molecules are broadly divided into physical and chemical agents. Physical sunscreens reflect and scatter UVB, UVA and visible radiation. Chemical sunscreens act by absorbing ultraviolet radiation and re-emitting chemical energy as heat or light. Several synthetic UV filter molecules are available in the market but they have limited use because these active molecules may create adverse effects on human skin. Some information on possible photon induced reaction such as photoirritation, photosensitization and contact dermatitis by sunscreen products containing synthetic organic sunscreen agents. To overcome these side effects, naturally occurring compounds have gained considerable attention as photoprotective agents. Flavonoids, a group of natural occurring compounds, act as catalysts in the light phase of photosynthesis and as stress protectants in plant cells by scavenging reactive oxygen species (ROS). Natural flavonoids have the potential photoprotection because of their UV absorbing, their ability to act as direct and indirect antioxidants as well as anti-inflammatory and immunomodulatory agents which provide exciting platforms for the development of photoprotection. This review summarizes the structure and potential photoprotection activity of several natural flavonoids.