INTRODUCTION
Melatonin is synthesized primarily in the pineal gland, and in several extra-pineal sites including the retina, skin, bone marrow, cerebellum, and gastrointestinal tract.1 Melatonin acts primarily via G-protein coupled membrane receptors, MT1 and MT2, at target sites in the central nervous system. MT1 membrane receptors are also present in the outer and inner root sheaths of cutaneous keratinocytes and fibroblasts.2
Melatonin is known as the main regulator of circadian rhythm but has also been implicated in the modulation of hair growth, cycle regulation, and pigmentation in both animal and human studies. In vitro studies and use of long-term subcutaneous melatonin implants in large animals, such as goats and dogs, support the ability of melatonin to stimulate hair growth and density.3-6 However, even among the same animal species, such as minks, conflicting studies describe decrease or increase in hair growth following melatonin treatment.7
Melatonin supplements are popular over the counter option touted as a panacea for hair growth not only on social media but also on physician meeting platforms without much convincing evidence. In this systematic review, we identify and analyze evidence on the qualitative and quantitative effects of melatonin on hair growth in human clinical studies in an attempt to determine its use as a supplement that improves hair growth.
Melatonin is known as the main regulator of circadian rhythm but has also been implicated in the modulation of hair growth, cycle regulation, and pigmentation in both animal and human studies. In vitro studies and use of long-term subcutaneous melatonin implants in large animals, such as goats and dogs, support the ability of melatonin to stimulate hair growth and density.3-6 However, even among the same animal species, such as minks, conflicting studies describe decrease or increase in hair growth following melatonin treatment.7
Melatonin supplements are popular over the counter option touted as a panacea for hair growth not only on social media but also on physician meeting platforms without much convincing evidence. In this systematic review, we identify and analyze evidence on the qualitative and quantitative effects of melatonin on hair growth in human clinical studies in an attempt to determine its use as a supplement that improves hair growth.
MATERIALS AND METHODS
A primary literature search was conducted using the PubMed, Google Scholar, and Cochrane databases in March 2022 using search criteria (hair OR hair loss OR alopecia OR effluvium OR scalp) AND (melatonin). Initially, 234 articles from the years 1966 to 2021 were identified. Inclusion criteria were as follows: studies investigating melatonin supplementation in hair growth/loss cycles in human subjects, clinically relevant randomized controlled trials (RCT), cohort studies, cross-sectional studies, case reports, observational studies, case series, retrospective studies, and clinical trials. Exclusion criteria included studies not written in English and studies not conducted on human subjects. Following title/abstract screening and duplicate removal, 59 articles met the criteria for inclusion. These articles underwent full article evaluation, as shown in the PRISMA flow diagram.
