2. What exactly is DHT?

Dihydrotestosterone is a steroid hormone from the androgen family. It is made when testosterone is converted by 5𝝰-reductase. There are at least two main isoforms of this enzyme relevant to hair and skin:

• Type II, which is abundant in hair follicles and the prostate,
• Type I, found in sebaceous glands, epidermis, and liver.

DHT binds to the androgen receptor more tightly than testosterone and activates it more strongly. In tissues where 5𝝰-reductase is active, DHT is the dominant androgenic signal.

Think of testosterone as the main circulating androgen, and DHT as a powerful local amplifier in specific organs where 5𝝰-reductase is active.

3. DHT across a man’s life

3.1 Foetal life: building the blueprint

In the male fetus, DHT is essential for the normal development of the external genitalia. It helps the genital tubercle differentiate into a penis rather than a clitoris, shapes the scrotum and contributes to urethral closure.

Children born with a deficiency in the type II form of 5𝝰-reductase make very little DHT. Despite normal or near-normal testosterone, they may be born with ambiguous or feminised external genitalia. Puberty later reveals their underlying male biology as testosterone levels rise, but the early absence of DHT demonstrates its importance in genital formation.

3.2 Puberty: sculpting the outward male

At puberty, the testes produce more testosterone. In tissues with 5𝝰-reductase, DHT is generated in greater quantities and contributes to:

• growth of the penis and scrotum beyond their childhood size,
• the appearance of facial hair, body hair and pubic hair,
• increased sebum production, which often means acne,
• growth and maturation of the prostate,
• and the early stages of androgen-dependent changes in scalp and body hair distribution.

Testosterone and DHT together forge the external traits we recognise as male secondary sexual characteristics. If either is missing, the process is altered.

3.3 Adult life: local mischief, less systemic necessity

Once puberty is complete, the role of DHT changes.

Testosterone carries most of the weight for muscle mass, bone density, libido, and sperm production.

DHT continues to exert its influence mainly where 5𝝰-reductase is present in abundance: in the prostate, skin and hair follicles.

Studies of families with inherited 5𝝰-reductase deficiency, and of men treated with strong 5α-reductase inhibitors for years, show that:

• masculinity, libido and erections can persist with very low DHT, provided testosterone is adequate,
• the prostate remains small and urinary symptoms are reduced,
• body hair is often sparse, and male pattern baldness is absent or markedly reduced.

After puberty has done its job, DHT is less about making a man a man and more about maintaining prostate size (sometimes a little too enthusiastically), driving acne and sebum production in predisposed individuals, and nudging vulnerable scalp follicles towards miniaturisation.

It is a powerful hormone in the wrong place, at the wrong time, in the wrong follicle.

4. DHT in women

Women also produce androgens from the ovaries, adrenals and via peripheral conversion in skin and fat. DHT in women has subtler roles but is not irrelevant.

• It contributes to the development and maintenance of pubic and axillary hair.
• It influences the sebaceous glands, thereby affecting sebum production and acne.
• In high amounts or in women whose follicles are very sensitive, DHT (along with other androgens) contributes to hirsutism (excess facial/body hair) and female pattern hair loss.

In polycystic ovary syndrome (PCOS) and other hyperandrogenic states, total and free androgens are often elevated. Clinically, this can mean increased terminal hairs on the face, chest and abdomen, persistent acne, menstrual irregularity or anovulation and, for some, premature or more aggressive thinning through the mid-scalp.

However, many women with female pattern hair loss have entirely normal blood androgen levels. Here, the issue is less “too much DHT in the bloodstream” and more:

• more active 5𝝰-reductase and androgen receptors in certain scalp follicles,
• a shift in the local hormonal balance after pregnancy or at menopause, when oestrogenic protection wanes,
• and the same genetic variations that make follicles behave differently among individuals.

5. How DHT affects the hair follicle

The effect of DHT on hair depends on where the follicle is located and how it is genetically wired.

In androgen-dependent sites like the beard, chest and pubic area, androgens (including DHT) stimulate vellus hairs to become thicker, pigmented terminal hairs. As a result, hair becomes coarser and growth more robust.

In androgen-sensitive sites on the scalp (frontal, temporal, and vertex regions in genetically predisposed people):

• DHT acts in the opposite direction, promoting miniaturisation,
• each growth cycle produces slightly thinner, shorter hair,
• the anagen phase shrinks, telogen lengthens, and the anagen:telogen ratio worsens,
• over time, enough follicles shrink that coverage is visibly thinned.

The back and sides of the scalp, in contrast, usually show:

• lower androgen receptor expression and/or different 5-alpha reductase activity,
• relative resistance to DHT-driven miniaturisation,
• preserved density and calibre even in advanced male pattern baldness.

This regional difference underpins both the pattern of baldness and the logic of transplanting hair from the occiput (back of the head) to the front.

6. Evidence that DHT is central to pattern hair loss

Several lines of evidence point to DHT as a key driver of androgenetic alopecia.

6.1 Patterns and physiology

The classic male pattern (receding hairline and vertex thinning with preserved occipital fringe) mirrors the distribution of androgen-sensitive vs resistant follicles.

Histological studies show increased 5𝝰-reductase expression and androgen receptor density in the balding frontal/vertex scalp compared with the occipital scalp in men with AGA.

6.2 Experiments of nature

Men with a lifelong deficiency of type II 5α-reductase rarely develop male pattern baldness. Their prostates are tiny, and their body hair is sparse, but their testosterone levels and gender identity are male.

Historically, castrated men (or men who lose their testes before puberty) do not develop typical male pattern baldness. Conversely, androgen administration or replacement in such men can induce androgenic hair changes.

6.3 Drug interventions as indirect experiments

Men taking finasteride or dutasteride – drugs that lower DHT by inhibiting 5α-reductase – show slower hair loss and, in many cases, partial regrowth compared with placebo.

Reductions in scalp DHT achieved with these drugs correlate with improvements in hair counts and reversal of miniaturisation in clinical trials.

Taken together (regional follicle biology, genetic deficiencies, castration data and drug trials), a coherent picture emerges: These observations do not mean DHT is the only cause, but they strongly implicate it.

7. DHT in women’s hair loss: more than just “male hormones”

In women, the relationship is more nuanced, but DHT still matters.

• Female pattern hair loss (FPHL) shares histological similarities with male AGA: miniaturised follicles, shortened anagen, and varied shaft diameters.
• Studies show increased 5𝝰-reductase and androgen receptor expression in affected scalp areas in women with FPHL compared with unaffected controls.
• Women with overt hyperandrogenism (for example, PCOS) who have high circulating androgens are over-represented among those with aggressive or early-onset FPHL.

However, many women with FPHL have normal serum DHT and testosterone, and some women with biochemical hyperandrogenism never develop significant scalp thinning.

The difference lies in:

• follicular sensitivity – how strongly the follicle reacts to a given DHT exposure,
• local enzyme expression – how much 5𝝰-reductase is present in the scalp vs elsewhere,
• oestrogen balance – how protective oestrogens are before and after menopause.

This is why some postmenopausal women, without obvious hyperandrogenism, notice accelerated thinning: oestrogen levels fall, the androgen:oestrogen ratio shifts, and the same DHT that was previously manageable now becomes more influential at the follicle.

8. Why does it make sense to target DHT?

Given all of this, reducing DHT (especially in the scalp) becomes a logical therapeutic target for androgenetic alopecia.

If DHT accelerates miniaturisation in susceptible follicles, then reducing DHT should slow that process and, where follicles are not irreversibly shrunken, allow some reversal.

This is exactly what is observed with:

• 5α-reductase inhibitors in men (finasteride and dutasteride),
• topical DHT-lowering strategies,
• and, to a lesser extent, anti-androgens in women.

Crucially, targeted DHT reduction does not remove testosterone, and therefore does not, in most men, strip away fundamental male characteristics. Blocking DHT is more like turning down the gain on a specific channel than muting the entire system.

Where DHT is doing more harm than good, for example, in prostatic overgrowth and androgenetic alopecia, that trade-off is often acceptable. Where DHT is still contributing usefully (foetal genital development, puberty), blocking it would be harmful. This is why 5𝝰-reductase inhibitors are contraindicated in women who may become pregnant, and are generally not suitable before puberty in men.

9. What lowering DHT seems to spare – and what it can affect

The widespread use of 5𝝰-reductase inhibitors (5-ARIs) for prostate enlargement and hair loss provides us with a long-term observation of what happens when human DHT is suppressed:

• Men on long-term 5-ARIs for BPH or hair loss do not routinely lose their masculine identity, muscle or sexuality. Most continue normal lives.
• They do, however, show reduced prostate size, altered prostate-specific antigen (PSA) dynamics, improvements in urinary symptoms, and, in those with androgenetic alopecia, slower hair loss and sometimes regrowth.
• A minority report sexual or mood-related side-effects, which tells us that DHT does contribute something to sexual and psychological functioning in some men.
• Men with congenital 5-alpha reductase deficiency demonstrate that the body can adapt remarkably to low DHT if testosterone is sufficient, albeit with distinct phenotypic differences (outward characteristics derived from genetics)

This empirical experience supports the idea that:

• in adult men, DHT is important locally but not the sole pillar of systemic male health,
• reducing DHT in a targeted way can be beneficial for specific conditions like benign prostatic hyperplasia (BPH) and AGA, and:
• there is a personal and ethical dimension in deciding whether those benefits outweigh potential harms for any given person.

In women, we have less data, but enough to be cautious:

• postmenopausal women with FPHL can sometimes benefit from DHT-lowering therapies,
• premenopausal women risk foetal harm if they become pregnant while taking 5-ARIs, and long-term systemic DHT suppression in women is not well characterised in the literature.

10. Where this leaves treatment decisions

If you are a man with early or moderate pattern baldness, you now know that most of the mischief is occurring where DHT meets genetically sensitive follicles, that your occipital hair is naturally resistant, and that DHT is not the sole guardian of your manhood.

If you are a woman with FPHL or PCOS, then you know that DHT is a player, but the larger hormonal picture and follicular sensitivity matter just as much. Further, any systemic targeting of DHT has to be weighed against reproductive plans and broader endocrine health.

Understanding DHT raises the quality of the conversation from a simple explanation that a drug blocks a hormone that causes baldness to a more nuanced discussion of the biological changes taking place and the potential consequences involved.