Hair loss has a reputation as one of life's inevitabilities — something that happens, or does not happen, and there is not much to understand about it beyond which lottery you drew. The biology tells a more interesting story. Male pattern hair loss is driven by a specific hormonal mechanism, expressed through a genetic predisposition, and operates through a sequence of events at the level of individual follicles that is now well enough understood to be meaningfully interrupted.
Understanding the mechanism does not make the experience of losing hair easier. But it does make the landscape of treatment choices more coherent, and it clarifies why some interventions work and others — despite popular appeal — do not.
The Role of DHT
Dihydrotestosterone, or DHT, is a more potent derivative of testosterone produced in specific tissues throughout the body — most relevantly for this discussion, in the scalp. The conversion of testosterone to DHT is catalysed by an enzyme called 5-alpha reductase, which is particularly concentrated in skin cells, scalp tissue, and prostate cells.
DHT binds to androgen receptors in the dermal papilla cells at the base of hair follicles, and it is this binding that initiates the miniaturisation process in genetically susceptible follicles. The mechanism, as described in research published in the Journal of Investigative Dermatology, involves DHT shortening the anagen (growth) phase of the hair cycle and prolonging the telogen (resting) phase, so that each successive growth cycle produces a shorter, finer hair. Over repeated cycles — which operate on a two-to-six year timescale for individual follicles — the follicle progressively miniaturises until it produces only fine, unpigmented vellus hair, and eventually nothing at all.
Importantly, DHT itself is not the villain in some broader physiological sense. It is required for normal male development, prostate function, and a range of androgenic processes. The problem in androgenetic alopecia is not high DHT across the body — most men with significant hair loss have testosterone and DHT levels within normal ranges — it is the sensitivity of specific follicles to DHT's effects.
Why Some Men Are Susceptible and Others Are Not
Here is where genetics enters the picture. Research from the Nature Genetics journal and subsequent studies have identified variants in the androgen receptor (AR) gene on the X chromosome as strongly associated with male pattern baldness risk. These variants increase the sensitivity of androgen receptors in hair follicles to DHT, meaning the same circulating DHT level that causes little to no follicle response in one man produces significant miniaturisation in another.
This explains one of the most persistent misconceptions about hair loss: that high testosterone causes baldness. It does not — susceptibility to the local action of DHT in the scalp does. A man with average testosterone levels and high follicular androgen receptor sensitivity can experience dramatic hair loss, while a man with elevated testosterone and low receptor sensitivity maintains a full head of hair throughout his life. The relevant variable is not how much testosterone you produce but how sensitively your follicles respond to its metabolite.
Research on 5-alpha reductase activity adds another layer. Studies have found that men with androgenetic alopecia show higher 5-alpha reductase activity in frontal and vertex scalp skin compared to men without hair loss — even when systemic hormone levels are identical. This local enzymatic activity determines how much DHT is produced at the follicle level, and it varies between individuals and between different regions of the scalp, which is why the classic pattern — recession at the temples and thinning at the crown — is so consistent across affected men.
Why the Temples and Crown?
Follicles in the frontal and vertex scalp regions carry a significantly higher density of androgen receptors than follicles on the sides and back of the scalp. This is the anatomical reason for the "horseshoe" pattern: the follicles least sensitive to DHT — those at the sides and occiput — are the ones that survive. Hair transplantation exploits this fact directly, relocating DHT-resistant follicles from the back of the scalp to areas where susceptible follicles have been lost.
How Current Treatments Target the Mechanism
Understanding the biology makes the mechanism of existing treatments straightforward. Finasteride inhibits the 5-alpha reductase enzyme, reducing DHT production in the scalp and prostate by approximately 70% at the standard 1mg daily dose. Less DHT means less stimulation of androgen receptors in follicles, which slows or halts miniaturisation. It cannot reverse miniaturisation that has already occurred — follicles already lost do not return — but it effectively protects viable follicles from ongoing DHT-driven damage.
Minoxidil works through a different mechanism entirely: as a vasodilator and potassium channel opener, it improves blood flow to follicles and extends the anagen phase of the hair cycle. It does not address the DHT pathway, which is why combining it with finasteride — attacking both the cause and the symptom simultaneously — has consistently produced better outcomes in clinical trials than either treatment alone. A 2024 meta-analysis published in Frontiers in Medicine confirmed that combined finasteride-minoxidil therapy outperformed both monotherapies on hair density metrics at 24 weeks.
Emerging treatments, including low-level laser therapy (LLLT) and topical formulations designed to act locally rather than systemically, continue to expand the toolkit. But the core mechanism — DHT sensitivity in genetically predisposed follicles — remains the target around which any effective treatment must be built.
The Bottom Line
Male pattern hair loss is not random. It is the expression of a specific genetic susceptibility through a hormonal mechanism that is well understood and meaningfully interruptible — particularly at early stages, before miniaturisation has progressed significantly. Knowing the biology does not change the genetics you were handed. But it does mean you can have an evidence-based conversation about your options, with a clear understanding of what the available interventions actually do and why.
