What are retinoids?

Retinoids are structural analogs of vitamin A (retinol). Vitamin A is a fat-soluble vitamin that was first extracted from egg yolk in 1909. It can be obtained directly from the diet (e.g., liver) or produced from carotenoids, a pigmented precursor that is found in abundance in yellow vegetables such as carrots. Beta-carotene, the primary carotenoid found in carrots, is particularly efficient in its ability to be converted to vitamin A. The physiologic effects of vitamin A are broad, but the most important functions include tissue differentiation (especially epithelial tissues), general growth, visual function, and reproduction. Retinoids may be produced naturally during vitamin A metabolism, but most retinoids used in the treatment of skin diseases are synthetic. Synthetic retinoids are produced by changing either the polar end group, polyene side chain, or cyclic group of vitamin A. More than 1500 retinoids have been synthesized and tested for their biologic properties since 1968.