Vitamins and the skin: Vitamin A and retinoids in dermatology.

Vitamin A and analogs are widely used in dermatology, with retinoids being natural and synthetic vitamin A derivatives. Topical retinoids (especially tretinoin and tretinoin precursors) can diminish photoaging and contribute to the thickening and restoration of skin collagen. Retinoids used as therapeutic agents include oral retinoids (eg, isotretinoin, acitretin, alitretinoin, and bexarotene) and topical retinoids (eg, isotretinoin, tretinoin, adapalene, tazarotene, and trifarotene). Although retinoids have traditionally been used for skin disorders of keratinization, such as psoriasis, pityriasis rubra pilaris, Darier disease, and ichthyoses, there is a variety of indications of retinoids for the treatment of skin diseases, including diseases of the pilosebaceous unit such as acne vulgaris, pigmentary disorders such as melasma, or cutaneous malignancies such as cutaneous T-cell lymphoma. Other retinoids with distinct routes of administration (oral or topical) and distinct dosing or safety profiles are recommended for different skin disorders. We discuss the mode of action and indications of retinoids used as pharmacologic agents in dermatology and provide an update on their use, effectiveness, and tolerability.