DHT and hair loss: the hormone behind pattern balding

If you have read anything about male pattern baldness, you have probably seen the letters DHT. It is often described as the "enemy" of hair, but the real story is more interesting, and understanding it helps you make sense of the treatments on offer.

What is DHT?

DHT (dihydrotestosterone) is a male hormone, or androgen, made from testosterone. The conversion is controlled by an enzyme called 5-alpha reductase ¹. DHT is found in several tissues, including the prostate gland and the skin ¹.

Androgens are important for normal male development before birth and during puberty, and they help regulate hair growth and sex drive in both men and women ². DHT is not a harmful substance in itself; problems arise in hair follicles that are genetically sensitive to it.

How DHT affects hair

Each scalp hair normally grows for years before resting and shedding. In people with pattern hair loss:

• DHT is believed to shorten the growth (anagen) phase from the usual 3 to 6 years to just weeks or months ¹
• The follicles gradually shrink (miniaturise), producing fewer, finer and shorter hairs ¹
• This happens on the hair follicles of androgen-dependent areas, such as the temples, top and crown, in genetically susceptible people ³

Hair at the back and sides of the head is usually much less sensitive to DHT. That is why these areas tend to keep hair even in advanced baldness, and why hair transplants take follicles from there ⁴. See hair transplants.

High testosterone does not mean baldness

A common myth is that bald men have more testosterone or are "more masculine". In fact, male pattern hair loss occurs in men who are genetically predisposed to be more sensitive to the effects of DHT ¹. Two men with similar hormone levels can have very different hair, depending on their genes. See is hair loss genetic?

What about women?

Androgens also play a role in female pattern hair loss, but other factors that are not yet known are involved too ². Most women with female pattern hair loss have normal androgen levels in blood tests ⁵. A minority have signs of hormone excess, such as irregular periods, acne or excess body hair, which can point to conditions like polycystic ovary syndrome (PCOS) ⁵. See a widening part.

Medicines that lower DHT

Because DHT drives male pattern hair loss, medicines that block 5-alpha reductase are a standard treatment.

Finasteride

• Finasteride is a 5-alpha reductase inhibitor taken as a tablet once a day. It treats male pattern hair loss by blocking the production of a male hormone in the scalp ⁶
• It may take at least 3 months to see any improvement, and you should expect to see improvement within the first 12 months. If there is no improvement after 12 months, further treatment probably will not help ⁶
• It only slows hair loss while you take it. Hair that grew back is likely to be lost within 12 months of stopping ⁶
• Women who are or may become pregnant must not handle crushed or broken tablets ⁶

Dutasteride

Dutasteride is another 5-alpha reductase inhibitor. DermNet lists finasteride and dutasteride among the treatment options for male pattern hair loss ¹. A 2022 network meta-analysis of 23 studies compared minoxidil, finasteride and dutasteride in men, and found that the relative results differed depending on the dose and the time point measured ⁷.

Side effects to know about

DHT-lowering medicines are generally well tolerated, but they are not free of side effects:

• A meta-analysis of 15 randomised placebo-controlled trials (4,495 men) found that these medicines carried a 1.57-fold risk of sexual dysfunction compared with placebo ⁸
• MedlinePlus lists sexual side effects, and also mentions a possible increased risk of a serious form of prostate cancer and reports of depression ⁶

Talk to a doctor about your own risks and benefits before starting, and report any mood changes promptly.

Minoxidil works differently

Minoxidil does not act on DHT. It is applied to the scalp and helps hair growth in a different way ⁹. Some people use it alone, and some use it together with a DHT-lowering medicine under medical advice ¹.

"Natural DHT blockers"

Many shampoos and supplements are marketed as "natural DHT blockers". The evidence summarised in this article relates to prescription medicines that have been tested in clinical trials. Be cautious of products that use the term DHT in their marketing without strong evidence behind them.

Signs that your hair loss may be DHT-related

• A receding hairline at the temples or thinning at the crown (in men). See a receding hairline and crown thinning
• A widening parting on top (in women)
• Gradual change over years, often with a family history
• Hairs that become finer and shorter before they are lost

Sudden shedding all over the head is more likely to have another cause, such as illness or stress. See sudden hair fall.

The bottom line

DHT is a key hormone behind pattern balding, but it only causes hair loss in follicles that are genetically sensitive to it. Medicines that lower DHT can slow male pattern hair loss, but they only work while you take them and they have possible side effects. A doctor can confirm the diagnosis and help you weigh your options. To understand how far hair loss has progressed, see the Norwood scale.

Frequently asked questions

What does DHT do to hair?

In sensitive follicles, DHT shortens the growth phase and makes follicles shrink, producing finer, shorter hairs ¹.

Do bald men have more testosterone?

Not necessarily. Pattern hair loss occurs in men who are genetically more sensitive to DHT ¹.

How long does finasteride take to work?

It may take at least 3 months to see improvement, with improvement expected within 12 months ⁶.

Does finasteride have side effects?

Yes. A meta-analysis found a 1.57-fold risk of sexual dysfunction versus placebo ⁸. Discuss the risks with a doctor.

Educational content. Not medical advice.