Melatonin and the Hair Follicle

Melatonin, primarily produced by the pineal gland, has been recognized for its role in influencing hair growth, pigmentation, and molting across various species, linking these processes to changes in the environment and reproductive cycles. Recent findings have identified specific melatonin receptors, MT2 and RORalpha, in murine hair follicles (HFs), although MT1 is not found in mouse skin. Human and murine skin, particularly human scalp HFs in the growth phase (anagen), have been shown to synthesize melatonin, a process that is increased by catecholamines. Melatonin appears to be involved in hair cycle regulation by decreasing apoptosis and estrogen receptor-alpha expression and by altering MT2 and RORalpha expression in a cycle-dependent manner. Additionally, due to its antioxidant properties and ability to induce DNA repair, melatonin may be produced within the hair bulb during the anagen phase as a protective mechanism against metabolic and proliferative stress.