How does minoxidil work? A plain-English explanation

Most people who try minoxidil know it’s meant to help thinning hair. Far fewer know what it’s actually doing on their scalp every day. It’s worth understanding, because it explains the three things that catch people out: the early shed, the long wait, and what happens if you stop.

From blood pressure tablet to scalp treatment

Minoxidil was developed in the 1970s as a tablet for severe high blood pressure. Doctors noticed an unexpected side effect: patients were growing more hair, sometimes in places they didn’t want it. That led to a version you apply to the scalp, which went on sale in the late 1980s. Today it’s one of the two main treatments for pattern hair loss.

What’s going on in a thinning scalp

Every hair grows from a follicle that works in cycles. A hair grows for two to seven years, stops for a couple of weeks, then rests for around three months before it falls out and the follicle starts again. Losing 50 to 100 hairs a day is normal.

In pattern hair loss, a hormone called dihydrotestosterone (DHT) gradually shrinks follicles in areas that are genetically sensitive to it. Dermatologists call this miniaturisation. Each cycle gets shorter and each new hair comes through finer and lighter, until some follicles produce little more than fuzz. The British Association of Dermatologists puts the cause down to a combination of genes and hormones, with more than 190 genes linked to it in men.

It’s very common. Around half of men are affected by their fifties. In women it usually appears later, often in the fifties or sixties, as general thinning on top and a widening parting rather than a bald patch.

What minoxidil does

Researchers still don’t have the complete picture, but the main effects are well described:

• It wakes resting follicles sooner. Follicles in the resting phase move into a new growth phase earlier than they would on their own.
• It keeps hairs growing for longer. A longer growth phase gives each hair more time to get long and thick before it stops.
• It can enlarge shrunken follicles. Over months, some miniaturised follicles go back to producing thicker, darker hairs.
• It widens blood vessels. That was its original job as a blood pressure medicine. Better blood flow around the follicle is thought to be part of the effect, though probably not the whole story.

Why it works well for some people and not others

Minoxidil isn’t active when it goes on. An enzyme in the hair follicle, sulfotransferase, converts it into its active form, minoxidil sulphate. People have very different amounts of this enzyme in their scalp, and studies have found that those with more of it tend to respond better. It’s one reason two people using it the same way can get very different results.

Other things that make a difference:

• How long you’ve been thinning. Follicles that have only recently started shrinking respond better than ones that have been dormant for years.
• Where the thinning is. Most research has measured hair on the top and crown of the head. Results at a receding hairline and the temples tend to be weaker.
• How consistently you use it. Regularly missed applications are one of the main reasons people see little change.

What minoxidil can’t do

• It doesn’t block DHT. The underlying process carries on in the background. Minoxidil pushes back against it for as long as you use it.
• It isn’t a course you finish. If you stop, the extra hair it has been supporting is usually lost over the following months. UK dermatologists stress that any benefit lasts only as long as the treatment is used.
• It won’t bring back follicles that have gone. Smooth, shiny skin that has been bald for many years usually has few working follicles left.
• It won’t fix hair loss with a different cause. Patchy hair loss, shedding after an illness, low iron, thyroid problems and damage from tight hairstyles all need a different approach.

Why the first months are confusing

Because minoxidil pushes resting hairs out to make way for new growth, many people shed more than usual in the first four to six weeks. Then nothing much seems to happen for a while, because hair only grows about a centimetre a month. The British Association of Dermatologists advises using it for at least six months, and possibly up to twelve, before judging whether it’s working. We go into both in minoxidil shedding and how long minoxidil takes to work.

Before you start

See your GP first if your hair loss is sudden or patchy, your scalp is itchy, sore or scaly, it started after a new medicine, or you feel unwell in other ways. A GP can check for causes such as low iron or an underactive thyroid. If you have a heart condition, are pregnant or breastfeeding, or are under 18, talk to a GP or pharmacist before using minoxidil.

Want the whole picture in one place? Our free Thinning Hair Handbook covers why hair thins, when to see your GP, how minoxidil works, how to apply it and what to expect month by month. It comes with a printable photo tracker.

This is general information, not medical advice. If you’re not sure whether something is right for you, speak to your GP or a pharmacist.

Sources: NHS: Hair loss; British Association of Dermatologists: Male pattern hair loss (leaflet); British Association of Dermatologists: Female pattern hair loss (leaflet).