Men go bald primarily because their hair follicles are genetically sensitive to a hormone called DHT (dihydrotestosterone), which gradually shrinks those follicles until they can no longer produce visible hair. This process, called androgenetic alopecia or male pattern baldness, affects 30 to 50% of men by age 50. By age 70, fewer than 15% of men still have a full head of hair.
How DHT Shrinks Hair Follicles
Your body naturally converts testosterone into DHT using an enzyme in the skin. DHT itself isn’t the problem. Every man produces it. The issue is what happens when DHT reaches hair follicles that are genetically programmed to overreact to it.
In susceptible follicles, DHT binds to receptors and activates genes that cause the follicle to miniaturize. With each hair growth cycle, the follicle gets slightly smaller, produces a thinner strand, and spends less time in its active growth phase. Over years, thick terminal hairs are gradually replaced by fine, nearly invisible “peach fuzz” hairs. Eventually, the follicle shrinks so much that the hair it produces can’t even break through the skin’s surface.
DHT also erodes the layer of fat tissue surrounding the follicle, which further compresses it and accelerates the shrinking process. This is why balding is progressive: each cycle of hair growth leaves the follicle in slightly worse shape than the last.
Why Your Hair Growth Cycle Changes
Healthy hair spends most of its life in the anagen (growth) phase, which normally lasts two to six years. In a full head of hair, the ratio of growing hairs to resting hairs is roughly 12 to 1. In balding scalps, that ratio drops dramatically, closer to 5 to 1. That means far more follicles are sitting dormant at any given time, and the ones that are growing don’t stay active long enough to produce a full-length strand.
This shortened growth window is the core mechanism behind thinning. The hair doesn’t just fall out one day. It gets progressively finer and shorter over many cycles until it’s essentially invisible.
The Role of Genetics
The gene most strongly linked to male pattern baldness is the AR gene, which provides instructions for building androgen receptors. Variations in this gene create receptors that are more easily activated by DHT than normal, meaning the follicle responds more aggressively to the same hormone levels that don’t affect other men’s hair.
The AR gene sits on the X chromosome, which men inherit from their mothers. This is why people often say baldness “comes from your mother’s side.” There’s truth to that, but it’s not the whole picture. Androgenetic alopecia clusters in families on both sides, and researchers suspect multiple other genes are involved that haven’t been fully identified yet. Having a close relative with pattern hair loss on either side of your family increases your risk.
How Balding Typically Progresses
Dermatologists classify male pattern baldness using the Norwood scale, which maps seven stages of hair loss. The pattern is recognizable because it follows a predictable path driven by which follicles are most sensitive to DHT.
- Stage I–II: Minor recession at the temples, often so subtle it’s hard to notice. The hairline hasn’t moved back more than about 2 centimeters.
- Stage III: The temple recession deepens noticeably and may reach the middle of the scalp. This is usually the first stage men recognize as genuine hair loss.
- Stage IV: The hairline has receded well past the midpoint of the scalp, and thinning at the crown becomes more obvious.
- Stage V–VII: The thinning areas at the front and crown merge. What remains is the classic horseshoe pattern of hair around the sides and back of the head.
Not every man follows this sequence exactly. Some lose hair primarily from front to back without developing a separate bald spot at the crown, keeping scattered thin hairs across the affected area rather than clean patches of baldness.
Inflammation Plays a Bigger Role Than Expected
Male pattern baldness is technically classified as “non-inflammatory,” but that label is misleading. About half of balding scalp samples show infiltration of immune cells and signs of low-grade chronic inflammation around the follicles. This microinflammation appears to damage stem cells that are essential for hair regeneration.
One key player is prostaglandin D2, a signaling molecule found at significantly elevated levels in bald scalp tissue compared to areas that still have hair. Prostaglandin D2 actively inhibits hair growth. The presence of inflammation also affects how well treatments work: men with visible microinflammation in their bald scalp had only a 55% response rate to topical minoxidil, compared to 77% among those without inflammation.
Smoking and Other Accelerators
Genetics loads the gun, but lifestyle factors can pull the trigger faster. Smoking is the most well-documented accelerator of male pattern baldness. Men who smoke 20 or more cigarettes per day face a significantly higher risk of moderate to severe hair loss. One study found that heavy smokers (10 or more cigarettes daily) had roughly three times the risk of developing severe balding compared to non-smokers.
Nicotine constricts the tiny blood vessels that feed hair follicles, cutting off their nutrient supply. It also accumulates in hair tissue, promotes DNA damage, triggers local inflammation, and may directly activate cell death pathways in the cells that build the hair shaft. Twin studies confirm the effect: among genetically identical twins, the one with more pack-years of smoking consistently showed worse frontal hairline thinning.
How It Differs From Stress-Related Hair Loss
Not all hair loss in men is permanent. Telogen effluvium is a temporary shedding condition triggered by surgery, high fever, extreme stress, iron deficiency, or major dietary changes. It typically begins two to three months after the triggering event and involves losing more than 100 hairs per day, often in clumps.
The key differences: telogen effluvium can start at any age, comes on suddenly, doesn’t follow the temple-and-crown pattern, and the shed hairs are all of uniform thickness. Pattern baldness, by contrast, is gradual, follows a predictable geographic pattern on the scalp, and produces hairs of varying thickness as follicles miniaturize at different rates. With telogen effluvium, the follicles themselves remain healthy and hair typically regrows once the trigger is removed. With androgenetic alopecia, the follicles are structurally changing.
What Treatments Actually Achieve
The two FDA-approved treatments for male pattern baldness work through different mechanisms. Finasteride is a daily pill that blocks the enzyme converting testosterone to DHT, reducing DHT levels in the scalp. Minoxidil is a topical liquid or foam applied directly to the scalp that increases blood flow to follicles and extends the growth phase.
In a head-to-head comparison, finasteride produced visible hair regrowth in 80% of men, while topical minoxidil achieved regrowth in 52%. Both work best when started early, before follicles have fully miniaturized. Neither is a cure. They slow or partially reverse the process, but hair loss typically resumes if treatment stops.
Hair transplant surgery relocates DHT-resistant follicles from the back and sides of the scalp to balding areas. Because those follicles retain their genetic resistance to DHT, transplanted hair generally continues growing permanently in its new location.