We have always been told that the hormone dihydrotestosterone (DHT) is by far the dominant cause of male pattern hair loss (aka androgenetic alopecia). However, numerous other hormones have positive and negative effects on scalp hair growth. I only realized this fully after a new study found yet another hormone to have an impact on hair growth. See the bottom of this post for a full list.
Serotonin and Hair Loss
A July 2025 publication by the renowned Dr. Junji Fukuda’s team in Japan found that serotonin (5-hydroxytryptamine, 5-HT) activates hair growth related genes in dermal papilla (DP) cells. Serotonin is both a neurotransmitter and a hormone. It is often confused with dopamine, since both are neurotransmitters, hormones and feel good molecules. Note that an older 2014 study also found that 5-HT plays a role in regulating hair pigmentation and stress-induced depigmentation.
In this study, the authors mention that circulating serotonin is mainly produced via intestine-microbiome interactions. They also briefly discuss how the microbiome produces various factors and metabolites that influence hair growth and hair regression. This has become an interesting new area of hair loss research, including via related research into the use of live biotherapeutic products to treat hair and skin disorders.
Circulating Hormones and their Influence on Dermal Papilla Cells
One paragraph in the above study in regards to various hormones and their effect on hair growth caught my eye. Especially since I have covered a few of them on this blog (see highlighted links below) without realizing that the number has built up.
“Multiple circulating hormones influence DP cells. For example, dihydrotestosterone shortens the anagen phase of DP cells, while increased estrogen levels (e.g., during pregnancy) spur additional hair growth. Likewise, oxytocin and cortisol exert opposing effects on DP cells and hair growth, the former activating growth factor secretion (stimulatory) and the latter decreasing Gas6 expression (inhibitory). The circadian hormone melatonin promotes hair regeneration via activating Wnt signaling in DP cells. Research on novel hair growth-promoting hormones has accelerated worldwide in pharmaceutical and cosmetic industries, largely targeting these hormones.”
Other hormones that can affect hair growth include: the earlier mentioned serotonin; thyroid; growth hormone; testosterone; insulin and insulin-like growth factor (IGF); and prolactin.
Hormonal Influences on Dermal Papilla Cells
Below is a summary of all the hormones I have discussed in this post and their impact on hair growth (usually via impacting dermal papilla cells):
- Dihydrotestosterone = Negative (-).
- Estrogen = Positive (+).
- Oxytocin = Positive (+).
- Cortisol = Negative (-).
- Melatonin = Positive (+).
- Thyroid = Positive (+).
- Testosterone = Negative (-).
- IGF-1 = Positive (+).
- Prolactin = Negative (-).
- Serotonin = Positive (+).
Does anyone sell pure Serotonin (not 5-HTP or Tryptophan)?
Yes, theories that often lead to nothing, fortunately from time to time we come across the element of luck… let’s keep in mind that we only know 3% of what is in space, the rest are just hypotheses and theories…
What about estrogen topicals ?
In my ancedotal experience DHT has been the main culprit. I am have done drugs for a decade that increase Seretonin in the body and it didn’t do anything for my hairloss but fin/dut has halted it in its tracks. I am sure somebody on antidepressants can chime in.
Other hormones obviously could, and probably do, play a role, but it is clear that DHT is the main culprit, otherwise finasteride wouldn’t work so well. Another clear cause of MPB is the sensitivity to DHT of course. If you are not genetically prone to hair loss, DHT simply won’t do its dirty business.
It’s just another theory, not a cure. I think a lot of the discussion about hair loss is based on wrong conclusions.
There are a lot of drugs on the market in the pharmacy sector, which they should be safe. They should cure something, but they don’t and shouldn’t harm someone, but they do.
I would trust a scientist who invents a hair loss product that works. Until then, I am very sceptical about theories like this one.
You do understand that “just theories” are in fact scientist working on, or discovering truths about AGA? This is important work that is done to ultimately get to a cure. It was only after we understood how the 5Ar works in the body, that we develop finasteride and dutasteride to block it.
It’s only after we understand the role of hair follicle stem cells, that we can develop drugs like pp405.