Current Challenges in Photoprotection
New developments in topical antioxidants and oral and subcutaneous agents... with photoprotective and antiphotocarcinogenic properties could potentially provide addition modalities for protection against the effects of visible light and infrared radiation.
Traditional sunscreens provide effective protection against erythema but not similarly effective protection against the generation of reactive oxygen species (ROS) in the skin after exposure to UVR, especially UVA. Therefore, antioxidants are incorporated in many sunscreen products because of their ability to scavenge and reduce levels of ROS, the primary mediator of oxidative damage to the skin. Compared with sunscreen alone, the addition of antioxidants has been shown to suppress ROS formation by an additional 1.7-fold for SPF 4, and 2.4-fold for SPF 15 and 50 formulas, respectively.
The safety of sunscreens containing inorganic UV filters of titanium dioxide and zinc oxide nanoparticles (single particles of diameter \100 nm) came into question after both were shown to induce formation of free radicals in vitro on exposure to UVR, which could potentially damage viable cells in vivo. However, it should be noted that when used in sunscreen, nanoparticles are coated with materials to almost completely block emission of ROS into the skin and to reduce cytotoxicity by preventing adherence of the nanoparticles to cells.