Male pattern baldness happens because a hormone called DHT (dihydrotestosterone) gradually shrinks hair follicles on the top and front of your scalp until they can no longer produce visible hair. By age 35, about two-thirds of men experience some degree of noticeable hair loss, and by 50, roughly 85% have significantly thinning hair. It’s extremely common, deeply genetic, and follows a predictable pattern that scientists now understand in considerable detail.
How DHT Shrinks Your Hair Follicles
Your body converts a portion of testosterone into DHT using an enzyme found in skin, hair follicles, and the prostate. DHT is a more potent form of testosterone, and it’s useful during puberty for developing body hair, deepening the voice, and building muscle. But in genetically susceptible hair follicles, DHT binds to androgen receptors and triggers a slow, destructive process called miniaturization.
When DHT attaches to receptors in a hair follicle, it shortens the growth phase of the hair cycle. Normally, a follicle grows hair actively for up to four years before entering a brief resting phase. Under the influence of DHT, that growth window gets progressively shorter, sometimes shrinking to just weeks. Each cycle produces a thinner, shorter, lighter hair. Over many cycles, what was once a thick terminal hair becomes a fine, nearly invisible vellus hair, and eventually the follicle stops producing visible hair altogether.
This is why male pattern baldness doesn’t happen overnight. It’s a gradual process spanning years or decades, with each hair cycle producing a slightly weaker version of the hair before it. The follicles on the sides and back of your head have receptors that are far less sensitive to DHT, which is why those areas almost always keep their hair.
Why Genetics Determine Who Loses Hair
Not every man exposed to DHT goes bald. The difference is genetic. The single most important gene is the androgen receptor (AR) gene, located on the X chromosome, which you inherit from your mother. This gene is estimated to account for up to 40% of the total genetic risk for male pattern baldness. A nearby gene on the same chromosome, called EDA2R, adds to that risk. Because both sit on the X chromosome, your mother’s side of the family is a stronger predictor of hair loss than your father’s.
But it’s not purely maternal. Researchers have identified additional risk genes on chromosomes 2, 3, 5, and 12, which can come from either parent. This is why some men go bald despite having a full-haired maternal grandfather, and why others keep their hair even when baldness runs on their mother’s side. The condition is polygenic, meaning dozens of genetic variants combine to determine your follicles’ sensitivity to DHT, how much DHT your body produces, and how quickly miniaturization progresses.
The Role of Inflammation and Scalp Tension
For years, male pattern baldness was classified as a purely non-inflammatory form of hair loss. But microscopic studies tell a different story. In one study examining scalp tissue, nearly 88% of samples from men with pattern baldness showed clusters of immune cells surrounding the hair follicles. Inflammation was found adjacent to miniaturized follicles in 86% of cases. Most of this inflammation was mild, concentrated around the upper portions of the follicle rather than the root.
There’s also a hypothesis linking scalp anatomy to the characteristic pattern of hair loss. The top of the scalp is covered by a tight sheet of connective tissue called the galea aponeurotica. Some researchers propose that chronic mechanical tension from this tissue triggers low-grade inflammation, which in turn increases local DHT production. Over time, this leads to thickening and scarring around follicles, restricting blood flow, oxygen, and nutrients. If this model is accurate, it would help explain why hair loss follows such a specific geographic pattern on the scalp, sparing areas where scalp tension is lower.
Neither inflammation nor scalp tension alone causes baldness. They appear to work alongside DHT and genetic susceptibility, potentially accelerating a process that was already underway.
How Hair Loss Typically Progresses
Male pattern baldness follows a well-documented sequence measured by the Norwood scale, a seven-stage classification system. In the earliest stage, there’s no real change. Stage 2 involves slight recession at the temples, creating what’s often called a “mature hairline.” This is so common it’s considered a normal part of aging rather than true baldness.
Stage 3 is where clinically significant loss begins. The hairline recedes deeply at both temples, forming an M or V shape, and the recessed areas become bare or very sparse. Some men instead lose hair primarily at the crown (the vertex) while the front stays relatively intact. By stage 4, both the temples and crown are thinning, separated by a bridge of hair connecting to the sides. In the most advanced stages (6 and 7), only a horseshoe-shaped band of hair remains around the sides and back of the head, and even that hair may become fine and thin.
Not every man progresses through all seven stages. Some stabilize at stage 3 and stay there for decades. Others move from a full head of hair to stage 5 within a few years during their twenties. The speed and extent of progression depend on your specific genetic profile and hormone levels.
What Treatment Can Realistically Do
The two main treatments work by either blocking DHT or stimulating follicle activity. One is a pill that reduces DHT levels throughout the body by preventing testosterone from converting into DHT. The other is a topical liquid or foam applied directly to the scalp that extends the growth phase and increases blood flow to follicles. Both are most effective at slowing further loss and modestly regrowing hair in areas where follicles haven’t completely shut down.
Clinical data shows that combining both approaches into a single topical solution produces meaningful improvements in hair density and hair thickness compared to using either one alone. The combined approach roughly tripled the odds of marked improvement in clinical trials. Topical formulations also largely avoid the systemic side effects associated with oral DHT blockers, which cause sexual side effects in about 2 to 5% of users.
The critical factor is timing. Miniaturization is much easier to slow or reverse in its early stages, when follicles are still producing thin hair. Once a follicle has been dormant for several years, no medication can reliably revive it. This is why men who start treatment at the first signs of thinning generally see better results than those who wait until significant loss has occurred.