Table 1.

Retinoid uses in cosmetic and dermatological skin care treatments

Retinoids	Functions/mechanism of action	Application in cosmetic and dermatological treatment
Retinol (all-trans retinol)	Inhibits collagenase and MMP expression; stimulates collagen type 1 and GAGs synthesis	Anti-wrinkle treatments, improvement of texture, dyspigmentation, dryness, and fine lines
Retinoic acid (all-trans retinoic acid, tretinoin)	Stimulates the process of epidermal cell proliferation, accelerates the elimination of sebum remaining in ducts, therefore reducing inflammation in sebaceous glands; loosens connections among cells in stratum corneum and inhibits keratosis	Acne, psoriasis, chronic inflammation of hair follicles and sebaceous glands
Retinyl esters (retinyl acetate and palmitate)	First converts to retinol by cleavage of the ester bond, and then converts into retinoic acid, stimulates the epidermal cell proliferation, regulates the sebum	Antioxidant, wrinkles, stabilising properties
Retinaldehyde	First oxidizes to retinoic acid by retinaldehyde dehydrogenases (e.g., RALDH2) or some enzymes of the CYP family and then stimulates the epidermal cell proliferation	Stabilising properties, wrinkles, texture
Adapalene (naphthalenecarboxylic acid)	Changes gene expression and mRNA synthesis; it is a strong modulator of keratinization of hair follicle cells, modifies keratinocyte metabolism, increases their proliferation, and thus has a keratolytic effect	Acne, inflammation, excessive keratosis
Tazarotene	Receptor-specific retinoid regulates down markers of keratinocyte differentiation, keratinocyte proliferation and inflammation	Acne vulgaris, psoriasis, chronically photodamaged skin, photoprotection from sunlight