Animal and human studies have convincingly demonstrated significant photopro-tective effects of ''natural'' and synthetic antioxidants when applied topically before UVA and UVB exposure. However, particularly with respect to UVB-induced skin damage, the photoprotective effects of most antioxidants were modest as compared to sunscreens. More successful in preventing such damage were appropriate combinations of antioxidants resulting in a sustained antioxidant capacity of the skin, possibly due to antioxidant synergisms. On the other hand, regarding photoprotective effects against UVA-induced skin alterations, which are largely determined by oxidative processes (75,189-192), topical administration of antioxidants might be particularly promising (193-195). In fact, topical application of antioxidants resulted in a remarkable reduction of UVA-induced ROS generation in mice (134), and diminished UVA-induced polymorphous light eruption in humans (178). Furthermore, topical application of antioxidants, particularly of vitamin C, was reported to diminish PUVA-induced erythema and sunburn cell formation (128,138,150,155,156).
Since UVA- and UVB-induced skin damage is not solely dependent on ROS formation and their reaction with numerous skin biomolecules, topical (as well as systemic) antioxidant supplementation cannot be presumed to give complete photoprotection (196). Other ROS-independent processes, such as DNA dimer formation, will persist in causing skin damage, regardless of the effectiveness of the antioxidant(s) administered. Therefore, efficient sunscreens are indispensable in the effective prevention of skin photodamage. However, antioxidants, in combination with sunscreens (128) or anti-inflammatory agents (135), seem to be highly effective adjuncts increasing the safety and the efficacy of photopro-tective products.
We would like to thank Sherry Hsieh and Prof. Helmut Sies for important com- ja ments and valuable discussions of the manuscript. This work was supported by <
a postdoctoral fellowship from the Deutsche Forschungsgemeinschaft (Th 620/1 - «
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