Male Pattern Baldness (Androgenetic Alopecia): The Science

Male pattern baldness is a household phrase. The clinical name is androgenetic alopecia (AGA). They mean the same thing: a genetically inherited sensitivity of certain hair follicles to androgens, primarily dihydrotestosterone (DHT), that gradually shrinks those follicles until they stop producing visible hair. It is by far the most common cause of hair loss in adult men. Roughly half of men show visible signs by age 50, and the underlying process can begin as early as the late teens or twenties.

This page covers what is happening biologically at the follicle level, how the condition progresses, and the staging system clinicians use to track it.

The hormonal driver: DHT

Testosterone is converted into a more potent androgen called dihydrotestosterone (DHT) by an enzyme called 5-alpha-reductase. DHT plays important roles during development and adulthood, but on the scalp of men with androgenetic alopecia, it is also the central driver of hair loss.

Genetically susceptible follicles, primarily on the top, front, and crown of the scalp, have receptors that bind DHT readily. When DHT binds, it triggers a cascade that progressively shrinks the follicle, a process called miniaturization. The follicles on the back and sides of the head are genetically resistant to DHT and do not undergo the same shrinkage, which is why androgenetic alopecia produces a recognizable pattern: vulnerable follicles thin out while resistant ones at the sides and back are spared. It is also why transplant surgeons take grafts from the back and sides.

For the full mechanism, see our companion page on DHT and hair loss.

What miniaturization actually looks like

A healthy follicle cycles through three phases:

• Anagen, the active growth phase, lasting two to six years.
• Catagen, a brief transition phase of about two weeks.
• Telogen, a resting phase of two to four months, after which the hair sheds and a new one grows from the same follicle.

In a healthy scalp, around 85 to 90 percent of follicles are in anagen at any given time, producing the thick, pigmented hair you see.

In androgenetic alopecia, DHT progressively shortens the anagen phase. Each successive cycle, the new hair grows for less time, so it ends up shorter, thinner, and lighter in color. The follicle itself also shrinks. Eventually the cycles get so short that the hair is barely visible (sometimes called vellus or peach-fuzz hair), and at the end stage the follicle stops producing visible hair entirely.

This is critical to understand: the follicle does not disappear instantly. It dies a slow death over years. Treatment can intervene at any point along that curve, but the earlier you start, the more follicles are still producing visible hair worth saving. The mechanism is covered in detail on the follicle miniaturization page.

The Norwood scale: how progression is staged

Clinicians and researchers use the Norwood-Hamilton scale to describe how far male pattern hair loss has progressed. It runs from Stage 1 (no visible loss) to Stage 7 (advanced, with only the horseshoe of hair around the sides and back remaining).

Roughly:

• Stage 1: full hair, no visible recession. The baseline.
• Stage 2: slight recession at the temples, often normal maturation of the hairline rather than true pattern loss.
• Stage 3: clear M-shaped recession at the temples. This is generally considered the first stage of true pattern hair loss. Stage 3v adds early thinning at the crown.
• Stage 4: deeper temple recession plus an obvious thinning patch on the crown, with a band of hair still separating them.
• Stage 5: the temple and crown areas start to merge as the band between them thins.
• Stage 6: the band is essentially gone, with significant baldness across the top of the scalp.
• Stage 7: only the horseshoe of hair around the sides and back remains.

Most men who develop androgenetic alopecia do not progress all the way to Stage 7, and the pace of progression varies a lot. Some men sit at Stage 3 for decades; others move from Stage 3 to Stage 5 in a handful of years. Our Norwood scale page covers staging in more depth.

The genetics of it

Androgenetic alopecia is highly heritable. Twin studies suggest the heritability is about 80 percent. The genes involved are spread across multiple chromosomes, but the most important known marker is on the X chromosome, which men inherit from their mothers. The popular advice to look at your maternal grandfather is based on this finding, but it is an oversimplification: paternal genes matter too, and so do many smaller-effect genes across both lineages (Hagenaars et al., PLOS Genetics, 2017).

Family history is informative but not deterministic. Plenty of men with bald fathers and grandfathers keep most of their hair, and plenty of men from unbalding families lose theirs. If hair matters to you, the more useful strategy is to track your own scalp with photographs and consult a physician at the first signs of recession or thinning rather than predict the future from a family tree.

Why androgenetic alopecia matters as a label

The clinical name distinguishes pattern hair loss from other types that can look similar but require different treatment:

• Telogen effluvium (stress-triggered diffuse shedding) resolves on its own once the trigger is removed.
• Alopecia areata (autoimmune patchy loss) requires immunomodulatory treatment, often topical or intralesional corticosteroids.
• Scarring alopecias (where follicles are destroyed by inflammation) can progress to permanent loss and require dermatologist evaluation.
• Traction alopecia (from prolonged tension on hair) requires removing the tension, not medication.

Establishing that what you have is androgenetic alopecia is the first job of a physician reviewing your case. It is the type with the strongest, most predictable response to telehealth-friendly medications.

Treatments that target the underlying process

Because androgenetic alopecia has a clear biological mechanism (DHT-driven follicle miniaturization), the most effective treatments target that mechanism directly.

5-alpha-reductase inhibitors block the enzyme that converts testosterone to DHT, lowering scalp DHT levels significantly:

• Finasteride at 1 mg daily blocks Type 2 5-alpha-reductase and is the most prescribed drug for AGA. It reduces scalp DHT by roughly 60 to 70 percent.
• Dutasteride blocks both Type 1 and Type 2 5-alpha-reductase, lowering DHT more profoundly. It is used off-label for hair loss when finasteride alone is insufficient or to maximize results.

Minoxidil does not address DHT directly, but extends the active growth phase of the hair cycle and improves follicle size and pigmentation. It is used in topical or low-dose oral form and is most effective when combined with a 5-alpha-reductase inhibitor.

Microneedling is adjunctive: it can enhance absorption of topical minoxidil and may stimulate follicle activity directly. It is typically used one to two times per week with a fine-gauge dermaroller.

The common combination of finasteride plus topical (or low-dose oral) minoxidil has the strongest evidence base, and it is what most dermatologists recommend as a starting point for men with progressing AGA. The treatment options page walks through how clinicians decide between approaches.

What treatment can and cannot do

A realistic frame for outcomes:

• What treatment does well: stops or slows progression in the large majority of patients who use it consistently. Often produces visible regrowth in areas where follicles are still active (Norwood 2 to 4, sometimes 5).
• What treatment does less well: reverses fully advanced loss (Norwood 6 to 7). At those stages, follicles in the bald regions have typically been miniaturized to the point of inactivity, and medication cannot reliably bring them back. Hair transplants, which move DHT-resistant follicles from the back of the scalp to the front, are the option at that point.
• What treatment cannot do: change the underlying genetics. As long as you have susceptible follicles and your body produces DHT, the process is ongoing. Stopping treatment means losing the hair that was preserved by it, usually within three to six months. Our what happens if you stop treatment page covers this in detail.

This is why androgenetic alopecia is a long-term management situation, not a one-time fix.

When to seek treatment

The honest answer is as soon as you notice recession at the temples, thinning at the crown, or a widening part. Earlier is better because more follicles are still producing visible hair, and those are the easiest to preserve.

A consultation with a licensed physician through a service like Curekey gives you a medical opinion on whether your hair loss is androgenetic alopecia, what stage you are at, and what combination of treatments fits your case. The broader hair loss in men overview covers the wider context.