Dihydrotestosterone (DHT) and hair loss: why the crown thins and the back does not

In short. Dihydrotestosterone (DHT) is an androgen that the enzyme 5-alpha-reductase produces from testosterone. It binds to the androgen receptor roughly five times more tightly than testosterone does. In people with a genetic predisposition, DHT triggers follicle miniaturization: with every cycle the hair becomes thinner, shorter and lighter, until it turns into almost invisible vellus down. Blood DHT levels usually stay normal – the deciding factor is not hormone concentration, but the sensitivity of specific follicles.

Patients often phrase the question this way: “I had my testosterone measured, it is normal, so why am I going bald?”. This is the most common misunderstanding around androgenic alopecia. Male pattern hair loss is almost never a disease of “hormone excess”. It is a story about local tissue sensitivity: the same androgens destroy a follicle in one scalp zone and leave it untouched in another.

Below we explain how DHT forms, what it does to the hair follicle at the cellular level, why the back of the head stays dense even in men with pronounced baldness, and which ways of influencing this mechanism have evidence behind them.

What dihydrotestosterone is and where it comes from

Dihydrotestosterone is the active form of the male sex hormone. The body does not produce it directly in large amounts: DHT forms from testosterone through the enzyme 5-alpha-reductase. The reaction occurs not only in the testes, but also directly in target tissues: the prostate, the sebaceous glands of the skin and the hair follicle.

The enzyme exists in three isoforms. Type one dominates in sebaceous glands and skin, type two – in the hair follicle and the prostate, while type three was discovered later and remains less studied. Type two matters most for hair loss, and finasteride targets exactly this isoform.

The key property of DHT is binding strength. It holds onto the androgen receptor about five times more firmly than testosterone and switches on androgen-dependent genes roughly ten times more actively. Even a small local concentration of DHT therefore produces an effect that testosterone at the same dose cannot.

• Testosterone: circulates in the blood, affects muscle, libido and bone tissue, and serves as raw material for the follicle.
• 5-alpha-reductase: the converting enzyme, works inside the tissue, and its activity is elevated in balding zones.
• DHT: the end product and the main androgen in the pathogenesis of androgenic alopecia.
• Androgen receptor: a protein inside the cell that receives the signal; its quantity and sensitivity are set genetically.

How DHT shrinks the follicle: the mechanism of miniaturization

The hair follicle lives in cycles: anagen (active growth, 2–6 years), catagen (transition, several weeks), telogen (rest, about three months). Hair length and thickness depend directly on how long anagen lasts.

DHT enters the cells of the dermal papilla – the control center of the follicle – and binds to the androgen receptor there. The complex moves into the nucleus and changes gene activity, suppressing the Wnt/beta-catenin signaling pathway that lets the papilla sustain growth. The follicle receives a command to shorten its growth phase.

The process then unfolds as follows. Each new anagen is shorter than the previous one, while the resting period grows longer. The hair no longer reaches its former length and thickness. Terminal hair gradually turns into intermediate hair, and then into vellus hair – thin, short and almost without pigment. Formally the follicle is still alive, but it no longer produces visible hair.

This explains the clinical picture that patients bring to the doctor. At first it is not the number of hairs that drops, but their quality: hair feels softer, holds styling poorly, and the part starts to show through in bright light. Visible thinning becomes obvious once some follicles have already gone through several cycles of miniaturization. You can read more about the stages of this process in our article on the Norwood-Hamilton scale.

Why the crown thins while the back of the head holds

DHT circulates evenly across the entire scalp. Yet baldness follows a recognizable pattern: temporal corners, the frontal hairline, the crown. The occipital and lateral zones stay dense even in men with advanced hair loss. The explanation lies not in the hormone, but in the properties of the follicles themselves.

Follicles of the frontal and parietal zone differ from occipital ones at the molecular level. The frontal zone has a higher density of androgen receptors – roughly one and a half times higher, according to comparative studies. It also shows higher activity of type two 5-alpha-reductase, so more DHT forms locally. Occipital follicles, by contrast, contain more aromatase, the enzyme that converts testosterone into estradiol and diverts it away from the “DHT pathway”. In addition, the androgen receptor gene in occipital cells is more heavily methylated, meaning it is partly switched off epigenetically. A comparison of dermal papilla cell cultures from two zones of the same person confirms these differences in a paper published in Scientific Reports.

This difference underlies the principle of donor dominance: a follicle keeps its properties after relocation. Hair moved from the back of the head continues to grow on the crown, because a change of address does not make it DHT-sensitive. Hair transplantation as a method with permanent results is built on this fact.

At the same time, a transplant does not stop the process in the patient’s own hair. If sensitive follicles around the transplanted area keep miniaturizing, new thinning may appear around the dense zone within a few years. Trichologists therefore treat surgery and medical support not as alternatives, but as parts of one plan.

The genetics of sensitivity: what is actually inherited

What you inherit is not “baldness” as such, but a set of follicle characteristics: the number of androgen receptors, enzyme activity, and the threshold of response to androgens. Review data from the NIH describe androgenic alopecia as a polygenic condition: large genomic studies have found hundreds of DNA regions linked to male pattern baldness.

The strongest single signal does indeed sit on the X chromosome, next to the androgen receptor gene. A man receives his X chromosome from his mother, which is where the popular idea “look at your mother’s father” comes from. The idea is partly fair, but incomplete: other significant loci sit on autosomes and pass down from both parents. Thick hair in your father is therefore no guarantee, and early baldness in your father is no verdict.

Genetics also determines the age of onset. In some men the first signs appear after the age of 20, and this is not a separate disease but the same mechanism starting early. We covered the factors that accelerate this debut in our article on the causes of early hair loss in men under 30.

Is a dihydrotestosterone blood test worth taking

This question comes up at every second consultation. For most men the answer is that a routine DHT blood test does not change treatment tactics. Serum hormone concentration correlates poorly with the degree of hair loss. Men with thick hair and men with pronounced baldness can show identical values, because the difference lies in the tissue, not in the blood.

Trichoscopy is far more informative: under magnification the doctor sees the spread of hair diameters in the thinning zone. Anisotrichosis, meaning the coexistence of thick and thin hairs in one area, is a direct sign of miniaturization and confirms the androgenic nature of the process.

Hormone testing becomes appropriate in other situations.

• Women with signs of hyperandrogenism: irregular cycles, acne, excessive hair growth on the face and body.
• Suspected polycystic ovary syndrome: a broader panel is then examined, not only DHT.
• Very rapid hair loss: when the picture develops over weeks rather than years.
• Hair loss in teenagers: endocrine pathology must be ruled out.
• Use of anabolic steroids or testosterone: an external source of androgens changes the calculation.

The scope of testing is defined by the doctor after an examination. You can book a trichologist consultation, where diagnosis is performed together with trichoscopy.

DHT and hair loss in women

The female body also produces testosterone and converts it into DHT, so androgenic alopecia occurs in women too. The pattern differs: instead of receding corners, the central part widens, while the frontal hairline is largely preserved. This is how androgenic alopecia presents in its female form.

The particular feature is that most female patients have normal blood androgen levels. Balance is what matters: estrogen levels fall after menopause, and the relative influence of androgens on the follicle grows without any change in their absolute concentration. Women also have higher aromatase activity in follicles, which partly explains the milder course of the process compared with men.

It is important to distinguish this mechanism from telogen effluvium after childbirth, rapid weight loss or illness. In those cases hair falls out massively and evenly, usually recovers on its own, and has no link to DHT. You can read more about the female scenario in our article on androgenic alopecia in women.

How the influence of DHT is reduced: what the evidence supports

You can affect the mechanism at two points: reduce DHT production or reduce the follicle response. Some popular products do neither, although they are sold under exactly this promise.

A classic study showed that finasteride at 1 mg lowers scalp DHT levels by roughly 64 percent and serum levels by roughly 71 percent according to a publication in the Journal of the American Academy of Dermatology. Dutasteride blocks all three isoforms of the enzyme and suppresses DHT more strongly, but it is not registered for alopecia treatment in every country.

Minoxidil deserves a separate mention, because it is often confused with a DHT blocker. It acts on blood vessels and on anagen duration, not on the hormone. The combination “DHT blocker plus minoxidil” is therefore logical: the drugs work at different points. We examined this product in our article on minoxidil, truth and myths.

Myths about DHT that get in the way of treatment

Plenty of false beliefs have accumulated around this topic. Three of them appear most often.

• “High testosterone means baldness”: in most men with hair loss androgens sit within the normal range, and receptor sensitivity is what matters.
• “A special shampoo washes DHT away”: the hormone forms inside the tissue, and a product that touches the skin for a few minutes does not change that process.
• “Once it starts, nothing can be done”: as long as the follicle is not replaced by connective tissue, it responds to treatment, and density can be restored surgically.

One more false belief concerns massage and “boosting circulation”. Blood supply does influence follicle nutrition, but it does not cancel the hormonal signal. We collected other widespread beliefs in a separate article on common myths about hair loss.

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