Retinoid

Retinoid is a class of chemical compounds derived from vitamin A that includes natural retinoids such as retinol, retinal, and retinoic acid, as well as synthetic analogs used therapeutically, including tretinoin, isotretinoin, adapalene, and tazarotene. Retinoids exert their effects mainly by binding to nuclear receptors known as retinoic acid receptors (RARs) and retinoid X receptors (RXRs), which regulate gene transcription involved in cell differentiation, proliferation, and apoptosis. Retinoic acid binds primarily to RARs, and RXRs form heterodimers with other nuclear receptors, enabling broad regulation of cellular processes. Vitamin A is also essential for vision, and retinoids influence development and immune function.

Clinically, topical retinoids are widely used in dermatology for acne, photoaging, and keratinization disorders because they promote orderly keratinocyte differentiation and reduce sebum production and comedone formation. Systemic retinoids, such as isotretinoin, are reserved for severe nodular acne and certain keratinization disorders but carry substantial adverse effects. In oncology, all-trans retinoic acid is used to treat acute promyelocytic leukemia by promoting maturation of malignant cells. Other systemic retinoids have roles in cancer therapy as part of combination regimens.

Retinoids are fat-soluble and vary in topical versus systemic use. Topical forms can cause irritation, dryness, and photosensitivity. Systemic retinoids can be teratogenic, cause lipid abnormalities, liver enzyme elevations, and mood or mood-related effects; pregnancy prevention and monitoring are required for many systemic agents. Dosing and monitoring depend on indication and formulation.

Historically, the link between vitamin A and health spurred development of synthetic retinoids in the 20th century, with tretinoin and isotretinoin among the first widely used agents, and regulatory controls for teratogenic risk evolving in the late 20th and early 21st centuries.