According to the article, you may be getting more hair and be less susceptible to sun damaged skin. What isn't clear is whether or not taking melatonin orally at typical dosage (300 mcg to 5 mg) will have those effects in humans. It seems that most of those human studies used topical application, and several of the animal studies used melatonin implants. Also, here is a quote from one of the references (Kleszczynski and Fischer, 2012):

> Regarding clinical application, exogenous melatonin should rather be used topically than orally, since orally administered melatonin appears in rather low levels in the blood due to prominent first-pass degradation in the liver, thus limiting skin access. Topical application might be meaningful, since melatonin can penetrate into the stratum corneum and build there a depot due to its distinct lipophilic chemical structure. Therefore, endogenous intracutaneous melatonin production, together with topically applied exogenous melatonin or metabolites can be expected to represent one of the most potent antioxidative defense systems against UV-induced skin aging.

>Melatonin administration has been found to increase hair growth in a variety of mammals

>In a randomized double-blind study of 40 women with hair loss, melatonin solution applied to the scalp increased hair growth significantly relative to placebo

Seems like a positive. The article is suggesting that by helping regulate the circadian rhythm, the use of melatonin can potentially: extend lifespan, prolong fertility, reduce cancer incidence, reduce obesity and insulin resistance, improve neurological recovery from brain injury, improve skin resistance to damage (such as from UV rays) and increase hair growth.

Unfortunately, this is unlikely to affect male pattern hair loss.

I have heard that the main questionmark is that typical doses are far larger than your body would normally produce, so you can't just assume it's "normal" or "natural".

But nobody has really identified harm yet.

Don’t see anything bad mentioned here.

TLDR: Animals with damaged pineal glands have trouble growing hair. Melatonin supplement helps reverse this. Topical melatonin reduces UV damage to the skin and can promote hair growth.

Nothing is bad in melatonin except the tolerance development. If I wasn't afraid of developing tolerance to endogenous melatonin I would take huge doses of it every evening.