Melatonina y fisiología capilar: Razones y datos de eficacia clínica como tratamiento tópico de la alopecia androgénica

Until quite recently, melatonin has been considered exclusively a hormone that regulates the circadian day-night rhythm and seasonal biorhythms. However, recent investigations have shown that melatonin has multiple activities, including antioxidant and anti inflammatory effects. In particular, human skin is not only a target of melatonin bioactivity, but also an important extra-pineal site of its synthesis, regulation and metabolism. Skin expresses the complete enzymatic apparatus necessary for melatonin biosynthesis. Therefore, the skin is now considered a relevant extra-pineal site of melatonin local production. Furthermore, the skin is able to build an antioxidant barrier against stressors from the environment through its melatoninergic antioxidative system. Melatonin receptors are expressed in keratinocytes, melanocytes, and fibroblasts. Finally, cutaneous melatonin is implicated in hair growth regulation and skin barrier function. On the scalp hair, melatonin can mediate several positive actions on normal hair growth, e. g. promoting the anagen phase. Furthermore, melatonin may have anti-apoptotic properties for residual hair follicle cells by attenuation of oxidative stress. Clinical studies have shown that melatonin can also counteract testosterone-induced cell actions. Therefore, there is a strong rationale for the clinical use of melatonin in the management of alopecia treatments. Topical melatonin in a lotion formulation has shown to be beneficial in the treatment of androgenetic alopecia in both men and women. In this review, we emphasize the role of melatonin in skin physiology and, in particular, at the hair follicle level, as well as the available clinical evidence regarding the efficacy of topical melatonin in androgenetic alopecia.