Vitamin A in Skin and Hair: An Update

Vitamin A is a fat-soluble micronutrient necessary for the growth of healthy skin and hair. However, both too little and too much vitamin A has deleterious effects. Retinoic acid and retinal are the main active metabolites of vitamin A. Retinoic acid dose-dependently regulates hair follicle stem cells, influencing the functioning of the hair cycle, wound healing, and melanocyte stem cells. Retinoic acid also influences melanocyte differentiation and proliferation in a dose-dependent and temporal manner. Levels of retinoids decline when exposed to ultraviolet irradiation in the skin. Retinal is necessary for the phototransduction cascade that initiates melanogenesis but the source of that retinal is currently unknown. This review discusses new research on retinoids and their effects on the skin and hair.

Automated summary

Vitamin A is essential for the growth of healthy skin and hair, but excessive or inadequate intake can have detrimental effects. Retinoic acid and retinal are the active metabolites of vitamin A, regulating the functioning of hair follicle stem cells, the hair cycle, wound healing, and melanocyte differentiation and proliferation. UV exposure lowers retinoid levels in the skin, and the source of retinal for melanogenesis initiation is currently unknown.