DHT and Male Pattern Baldness: The Mechanism, Explained Properly

Marco was 26 when he first noticed his hairline moving. He wasn’t stressed, wasn’t washing his hair excessively, wasn’t wearing hats. His scalp was clean, his circulation was fine. His doctor told him it was “just genetics” and left it there. That answer is technically right and practically useless. The genetics operate through a specific, well-understood molecular pathway, and if you know how that pathway works you can think clearly about what to do about it.

Related on the Blueprint: Dutasteride vs Finasteride and Finasteride Side Effects.

This article walks through that pathway. No hand-waving, no myths. Just the mechanism, the evidence, and an honest look at what it means for treatment.

First, kill the myths

Androgenetic alopecia (AGA), which is the clinical name for male pattern baldness, is not caused by poor scalp circulation. Not by hats. Not by shampooing too often. Not by clogged follicles. These ideas persist because baldness still carries enough stigma that people reach for controllable explanations. The actual driver is a genetically determined sensitivity inside certain follicles to a hormone called dihydrotestosterone, or DHT.^[3]

That last phrase matters: sensitivity, not amount. I’ll come back to it because it’s the single most clarifying idea in this whole field.

What DHT actually is and where it comes from

DHT is an androgen, a male sex hormone, derived from testosterone. The conversion happens via an enzyme called 5-alpha-reductase, which comes in two main forms. Type I is found mostly in skin and sebaceous glands. Type II is concentrated in hair follicles and the prostate. Both types can perform the conversion, but type II is the primary one operating inside the follicle itself.^[3]

Once DHT is made, it binds to the androgen receptor (AR) sitting in the dermal papilla, a cluster of specialized cells at the base of each hair follicle. The dermal papilla controls whether that follicle grows, rests, or shrinks. When DHT locks into the androgen receptor in a sensitive follicle, it triggers a cascade of signaling that progressively shortens the follicle’s growth phase and reduces the follicle’s physical size. The result, played out over years, is miniaturization: thick, pigmented terminal hairs becoming progressively thinner and shorter, until they’re barely visible vellus hairs, and then eventually nothing at all.

Why it’s “sensitivity,” not amount

Here is the part that most coverage misses. Plenty of bald men have completely normal testosterone levels. Their total androgen load is no different from a man with a full head of hair. The difference is in the follicle itself: some follicles are wired to react strongly to DHT, and some aren’t.

Think of it this way. DHT is the sunlight. The follicle’s genetic makeup is how easily it sunburns. Two men can stand in exactly the same sun for the same amount of time. One turns red immediately. The other walks away fine. The sun didn’t change; the skin’s response did. That’s the same logic behind why two brothers with identical testosterone levels can have very different hairlines in their thirties.

This reframes the entire treatment logic. You’re not trying to fix a hormone problem. The hormone is fine. You’re trying to reduce the signal reaching a follicle that’s been told by its genetics to overreact to that signal.

The pattern: why it forms where it does

Androgenetic alopecia has a recognizable shape. The frontal hairline retreats. The vertex thins. The crown opens up. But the sides and back, the occipital region, generally stay put. Why? Because occipital follicles are relatively DHT-resistant. They have fewer androgen receptors, or those receptors respond differently, or both. The same DHT that miniaturizes a vertex follicle largely leaves the occipital follicle alone.^[3]

This regional difference is also why hair transplants work. Surgeons harvest grafts from the occipital donor zone specifically because those follicles carry their DHT-resistance with them. When you move an occipital follicle to the frontal scalp, it keeps growing there. This is called donor dominance, and it’s proof that the sensitivity is coded in the follicle, not determined by its location on the scalp.

The genetics: what “it runs in your family” actually means

AGA is strongly heritable and polygenic, meaning many genes contribute. The androgen receptor gene sits on the X chromosome, which is why the maternal grandfather comparison has a grain of truth to it. But the X-chromosome story is massively oversimplified. Genome-wide association studies have now identified dozens of loci associated with AGA spread across multiple chromosomes, and the predictive value of any single locus is modest.^[3]

The practical upshot: you can’t reliably predict who will lose hair and how much based on family trees. You can say the odds are elevated if multiple relatives are affected on both sides. Roughly half of men show noticeable AGA by age 50. That number has been replicated across different populations enough that it’s a reasonable baseline, not a scare figure.

What genetics determines, ultimately, is how many of your scalp follicles carry androgen receptors calibrated to respond aggressively to DHT, and how that sensitivity changes as DHT exposure accumulates across decades. A man who starts losing hair at 20 has typically inherited a more widespread and more reactive sensitivity than a man who notices it at 45.

Miniaturization, step by step

The hair cycle has three main phases: anagen (growth, lasting two to six years in a healthy follicle), catagen (a brief transition), and telogen (rest, then shedding). In AGA, DHT binding the androgen receptor in the dermal papilla progressively shortens the anagen phase. Less time growing means less hair grown per cycle, and a smaller follicle means a finer, shorter hair each time.

This is gradual. It’s not that you go to bed with one hairline and wake up with another. Each hair cycle takes months. The change only becomes visible after enough cycles have compounded. That’s why men often don’t notice until there’s already meaningful loss. The process was running quietly for years before the mirror gave it away.

There’s also a point of no return. A follicle that has been miniaturizing for a long time can reach a state where it’s essentially dormant, the dermal papilla no longer responsive enough to generate a proper hair. Lower the DHT at that stage and the follicle may not come back. This is the single strongest argument for acting early rather than waiting to see how bad it gets.^[1]

Why the treatments work where they do

Once you understand the mechanism, the treatment logic is straightforward. Two main pharmacological approaches exist, and they operate through completely different routes.

Finasteride and dutasteride both lower DHT. Finasteride blocks 5-alpha-reductase type II and reduces serum DHT by roughly 70 percent. Dutasteride blocks both type I and type II and suppresses serum DHT by about 90 percent.^[1][2] Less DHT reaching the androgen receptor means less signal driving miniaturization. The follicle doesn’t regrow overnight; but the ongoing cycle-by-cycle shrinkage slows or stops, and in some cases partly reverses where follicles weren’t yet dormant.

Minoxidil works differently. It doesn’t touch DHT at all. Instead it extends the anagen phase directly, keeping follicles in active growth for longer. It also increases blood flow to the scalp, though that’s probably a secondary effect rather than the mechanism. Because it bypasses the DHT pathway entirely, it’s useful even in women with hair loss and as an adjunct when DHT-lowering drugs plateau.^[3]

Neither drug reverses advanced loss. A slick-bald scalp where follicles have been dormant for years is unlikely to respond. The follicle biology is gone. The reason to treat early is exactly to prevent arriving at that point. The follicle you protect now is worth far more than any regrowth campaign later.

What doesn’t work, and why people keep trying it

Scalp massage, castor oil, ketoconazole shampoo (for the main loss, not dandruff control), microneedling as a standalone: none of these address the DHT-androgen receptor axis. Some might have minor adjunct effects or improve the scalp environment, but they cannot slow the core mechanism driving miniaturization. People reach for them because they’re controllable, accessible, and carry no prescription friction. That’s understandable. But understanding the mechanism makes it clear why they can’t substitute for interventions that actually interrupt the pathway.

The circulation myth is worth addressing specifically. The pattern of loss doesn’t follow poor circulation. If it did, the back and sides would thin too. They don’t. The pattern follows regional follicle sensitivity to DHT. That is the mechanism.

The honest uncertainty

The core pathway is well established. Where things get murkier is at the edges. We don’t have precise tools to predict at 25 how severe a man’s loss will be by 45. We know DHT is the driver, but we can’t yet measure an individual follicle’s androgen receptor sensitivity before it starts showing symptoms. We also know that DHT suppression works better in some men than others, and we can’t perfectly predict who will be a strong responder before treatment starts.

The genetics research is advancing but hasn’t reached clinical utility yet. A polygenic score for AGA may eventually give early warning, but we’re not there. What we have now is a clear mechanism, effective tools for slowing it, and a time-sensitive window. Knowing that is enough to make a reasoned decision.

If you want to go deeper on the biology and treatment evidence, including my review comparing finasteride and dutasteride in AGA, you’ll find it at philippeb.pro.