Tropospheric ozone: an emerging environmental stress to skin

As the outermost barrier of the body, the skin is directly and frequently exposed to a prooxidative environment, including solar UVA and UVB radiation, and air pollution. Ozone, a major air pollutant, possesses a strong oxidizing potential and therefore is possibly one of the most reactive chemicals the skin ever meets. Although a large body of evidence exists for ozone induced oxidative stress in the respiratory tract, the current knowledge of its in vivo effect on cutaneous tissues is very limited. Acute ozone exposure depletes skin vitamins C and E and induces lipid peroxidation in upper epidermal layers. The stratum corneum, as the penetration barrier of the body, appears to be particularly susceptible to ozone induced oxidative stress. Such processes at superficial skin layers lead to barrier perturbations and could trigger inflammatory responses in adjacent skin layers. Furthermore, there is some in vitro evidence for an involvement of ozone in cutaneous inflammation and carcinogenesis. Taken together, these findings may be particularly relevant for photochemical smog: concomitant exposure to UV-irradiation and ozone could reveal synergistic oxidative stress effects in skin. The mechanisms of ozone induced effects in cutaneous tissues are still poorly understood. Further studies in this young field of research are needed to evaluate its relevance for skin disorders in humans.