ABSTRACT
Carotenoids are a class of compounds which has never been identified as being essential for humans; there are no studies indicating that a completely carotenoidfree diet causes deficiency symptoms as long as preformed vitamin A is available in the food. Yet overwhelming evidence indicates that carotenoids play an important role in protecting the organism from many harmful reactions and noxious agents (for review see Chapters 16, 18 and 19). This applies also to the skin where carotenoids function both as potential provitamins A (e.g., beta-carotene and lutein) and as antioxidants or cellular signaling agents of particular importance in relation to UV irradiation, skin aging and carcinogenesis (see Chapters 17 and 18).
