The mechanism of action of topical retinoids.

UV irradiation of human skin sets in motion a complex sequence of events that causes damage to the dermal matrix. When topical tretinoin is applied to human skin, any collagen deficiency existing in photoaged skin is remedied at least partially, and the skin is primed to prevent further matrix degradation induced by solar UV. Retinoids, therefore, have become essential in the treatment and prevention of photoaging. This article describes the mechanism of action of retinoids, including how they are mediated through retinoic acid receptors (RARs) and retinoid X receptors (RXRs), how they block inflammation mediators, and how production of procollagen is increased to augment the formation of types I and III collagen. Three naturally occurring retinoids are reviewed.