For nearly a century, it has been recognized that vitamin A (i.e., retinol and its esters; Fig. 1) plays a critical role in the health of epithelial tissue. Clinical observations made by Bloch (1921) and experimental studies by Mori (1922) and Wolbach and Howe (1925) first established a link between a diet deficient in vitamin A and abnormal keratinization of epithelia. Since these early beginnings, studies on epithelial tissues and cells derived from them have provided an enormous amount of information on the roles of vitamin A in processes such as cellular division, diVerentiation, and transformation, as well as intracellular and intercellular signaling. The skin has been an epithelial tissue of particular interest as a target for the eVects of vitamin A and other retinoids. This is due to several reasons. The skin is an easily accessible tissue for in vivo studies, and the structure and function of the skin is dependent on retinoid-influenced orchestration of cellular division, diVerentiation, and keratinization. In addition, interest in the skin is undoubtedly driven by the potential for development of dermatological products and cosmetics containing retinoids. Today, a wide range of der-matologic disorders are treated with a number of geometric isomers of retinoic acid and structurally similar synthetic retinoids (Sekula-Gibbs et al., 2004). Retinoid-containing cosmetic products, particularly those marketed to reduce the appearance of skin aging and photoaging, continue to

The Mammoth Book of Bath and Beauty Recipes

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