Men go bald primarily because of a hormone called DHT (dihydrotestosterone), a potent byproduct of testosterone that gradually shrinks hair follicles until they can no longer produce visible hair. By age 35, two-thirds of men will have some degree of noticeable hair loss. By 50, roughly 85% will have significantly thinning hair. It’s overwhelmingly common, deeply genetic, and starts much earlier than most men expect.
How DHT Shrinks Your Hair Follicles
Testosterone itself doesn’t cause baldness. Your body converts a portion of testosterone into DHT through an enzyme in the skin. DHT then binds to receptors on hair follicles, particularly along the top of the scalp, and triggers a process called miniaturization. Follicles that once produced thick, healthy strands begin constricting. The growth phase of each hair cycle shortens, and the follicle starts producing thinner, more fragile hairs with weaker shafts that break or fall out easily.
Over successive cycles, the follicle shrinks further. What was once a full terminal hair becomes a fine, nearly invisible wispy strand. Eventually, the follicle may stop producing visible hair altogether. This process is gradual, often unfolding over years or decades, which is why many men don’t notice the change until significant thinning has already occurred. The follicles on the sides and back of the head are naturally resistant to DHT, which is why those areas tend to keep their hair even in advanced baldness.
Genetics Are More Complex Than You Think
You’ve probably heard that baldness comes from your mother’s side. That’s a half-truth. The most well-established gene involved in male pattern baldness is the AR gene, which sits on the X chromosome (the one you inherit from your mother). This gene provides instructions for building androgen receptors, the docking stations that DHT latches onto. Variations in the AR gene can make those receptors more sensitive to DHT than normal, meaning even typical hormone levels cause follicles to shrink.
But the AR gene isn’t the whole story. Researchers suspect that variants in several other genes also contribute, and the condition clearly clusters in families on both sides. Having a close relative with patterned hair loss, whether that’s your father, grandfather, or uncle, increases your risk regardless of which side they’re on. The inheritance pattern is complicated enough that no genetic test can reliably predict exactly how much hair you’ll lose or when.
Why Some Men Lose Hair Earlier
Genetics set the stage, but other factors can push hair loss to start sooner or progress faster. Smoking is one of the clearest accelerants. A 2020 study comparing male smokers and nonsmokers between ages 20 and 35 found striking differences: 47% of smokers had grade 3 hair loss and 24% had grade 4, while only 10% of nonsmokers reached those stages. Nicotine and related chemicals appear to damage hair follicles through two mechanisms. They increase free radical activity, creating oxidative stress that damages cell DNA. And they reduce blood flow to the scalp, disrupting collagen production and leaving hair brittle and undernourished.
Metabolic health also plays a role that’s often overlooked. Insulin resistance, the condition where your body stops responding efficiently to insulin, has been linked to earlier onset of male pattern baldness. Insulin appears to influence how your skin processes androgens like DHT, and metabolic syndrome (the cluster of conditions including high blood sugar, excess belly fat, and abnormal cholesterol) is significantly associated with early hair loss. For some men, thinning hair in their 20s may actually be an early signal of metabolic issues worth investigating.
What’s Happening on Your Scalp
The surface of your scalp hosts a complex community of microorganisms that influence hair health more than most people realize. In men with pattern baldness, levels of a fungus called Malassezia tend to be elevated. Higher Malassezia populations can trigger local immune responses and low-grade inflammation around the follicle, which may compound the miniaturization process already driven by DHT. This microinflammation doesn’t cause baldness on its own, but it can worsen the progression in follicles that are already vulnerable.
How Hair Loss Is Classified
Doctors use the Norwood scale, a seven-stage system, to describe the pattern and severity of male hair loss. Stage 1 shows no significant loss. Stage 2 involves mild recession at the temples, often called a “mature hairline,” which many men develop naturally and doesn’t necessarily mean progressive balding. Stages 3 through 5 show increasing recession and thinning on the crown, forming the familiar horseshoe pattern. Stages 6 and 7 represent extensive loss where the top of the scalp is largely bare.
Knowing where you fall on the scale matters because treatment works best in the earlier stages, when follicles are miniaturized but still alive. Once a follicle has been dormant for years, it’s much harder to revive.
Treatments That Actually Work
Two treatments have the strongest evidence behind them. Minoxidil, applied topically to the scalp, increases blood flow to follicles and extends the growth phase of the hair cycle. Used alone, about 25% of men see marked improvement, and roughly 48% see moderate improvement. It works best for maintaining what you have and producing modest regrowth.
Finasteride works differently. It’s taken as a pill and blocks the enzyme that converts testosterone into DHT, reducing DHT levels in the scalp. When combined with minoxidil, results improve substantially: about 53% of men see marked improvement and 70% see at least moderate improvement. Roughly 18% of men on the combination show no change at all, compared to 28% using minoxidil alone. Both treatments require ongoing use to maintain results. If you stop, the hair loss process typically resumes.
For men with more advanced loss, hair transplant surgery moves DHT-resistant follicles from the back of the head to thinning areas. The two main techniques differ in how follicles are harvested. Strip harvesting (FUT) removes a thin strip of scalp and dissects individual follicle units from it, achieving graft survival rates around 86%. The individual extraction method (FUE) removes follicles one by one, leaving no linear scar but historically showing lower survival rates, around 61 to 70% in comparative studies. Technique and surgeon experience matter enormously for outcomes with either approach.
Why Only the Top of the Head
One of the most common questions men have is why hair falls out on top but stays on the sides. The answer comes down to biology at the follicle level. Hair follicles in different parts of the scalp have different densities of androgen receptors. Follicles along the temples and crown are packed with receptors that respond strongly to DHT, making them vulnerable to miniaturization. Follicles on the sides and back of the head have far fewer of these receptors, so they’re largely unaffected even when DHT levels are high. This is also why transplanted hair from the back of the head continues to grow in its new location: it carries its original genetic resistance with it.