Skin antioxidants: their role in aging and in oxidative stress - New approaches for their evaluation

Skin is a highly metabolic tissue which possesses the largest surface area in the body and serves as the protective layer for internal organs [1]. Ski n is also a major candidate and target of oxidative stress. It is designed to give both physical and biochemical protection, and is equipped with a la rge number of defense mechanisms. The skin tissue is exposed to a variety o f damaging species which originate in the outer environment, in the shin it self, and in various endogenous sources [2, 3]. The structure of skin is qu ite complex being composed of several layers, each of which plays a specifi c role and carries out different functions [4]. Each layer is equipped with its own arsenal of defense molecules, and the various systems differ from each other based on the layer's susceptibility to oxidative stress and its function. It is generally agreed that one of the major and important contri butions to skin aging, skin disorders and skin diseases results from reacti ve oxygen species (ROS) [1, 5]. Due to the high occurrence of potential bio logical targets for oxidative damage, skin is very susceptible to such reac tions. For example, skin is rich in lipids, proteins, and DNA, all of which are extremely sensitive to the oxidation process [6-8]. Elucidation of the : mechanisms involved in skin oxidation and the examination of the defense systems may contribute to the under standing of skin aging and of the mecha nisms involved in the various pathological processes of skin. This review a ddresses the antioxidant defense mechanism of the skin, the rule it plays d uring the aging process, and the role skin has following exposure to oxidat ive stresses. (C) 1999 Elsevier, Paris.