The role of retinoids in the prevention and repair of aged and photoaged skin.

Retinoids, either naturally occurring or synthetic, are defined by their ability to bind nuclear retinoid receptors of the steroid/thyroid superfamily. Their protean but key function in physiology is control of cellular proliferation and differentiation. Topical retinoids, namely tretinoin, have been proven to prevent and repair clinical features of photoageing; these processes are facilitated by an ability to prevent loss of collagen from, and stimulate new collagen formation in, the papillary dermis of sun-exposed skin. Emerging evidence indicates that intrinsic, chronological ageing of the skin shares several mechanistic features with photoageing. Indeed aged skin is characterized by retinoid sensitivity and is probably reparable by application of topical retinoids.