Male pattern baldness is caused by a combination of genetics and a hormone called DHT (dihydrotestosterone), a byproduct of testosterone. About two-thirds of men will notice some degree of hair loss by age 35, and roughly 85% will have significantly thinning hair by 50. The process isn’t sudden. It unfolds over years as hormone-sensitive hair follicles gradually shrink, producing thinner and shorter strands until they stop producing visible hair altogether.
How DHT Shrinks Hair Follicles
Testosterone circulates through your bloodstream and gets converted into DHT by an enzyme in your skin and scalp. DHT is more potent than regular testosterone, and in men with a genetic susceptibility, it binds to receptors on hair follicles and triggers a process called miniaturization. The follicle physically shrinks. Each cycle of hair growth produces a strand that’s finer, shorter, and lighter than the one before it.
One of the most significant effects is on the growth phase of the hair cycle. A healthy hair follicle stays in its active growth phase for three to six years. DHT can shorten that window to just weeks or months. When follicles spend less time growing and more time resting, you see less coverage on the scalp. Eventually, the follicle becomes so small that it only produces a tiny, nearly invisible hair, or stops producing hair entirely.
What makes this confusing for many men is that DHT doesn’t affect all hair equally. The follicles on top of your head and at the temples are genetically programmed to be sensitive to DHT, while the follicles on the sides and back of your head are largely resistant. That’s why the classic horseshoe pattern of remaining hair develops, and why hair transplants can move DHT-resistant follicles from the back of the head to the top.
The Genetics Behind It
The single gene most clearly linked to male pattern baldness is the AR gene, which provides instructions for building androgen receptors. These receptors are what allow DHT to attach to and influence hair follicles. Variations in this gene can make your follicles more responsive to DHT, accelerating the miniaturization process. The AR gene sits on the X chromosome, which you inherit from your mother. That’s the origin of the old idea that baldness comes from your mother’s side of the family.
The reality is more complicated. Researchers suspect that variants in multiple genes contribute to hair loss risk, though only the AR gene has been confirmed through scientific studies. Because many genetic and environmental factors are involved, the inheritance pattern isn’t straightforward. You can inherit baldness-related genes from either parent. Having a bald father increases your risk, and having a bald maternal grandfather does too, but neither guarantees anything. Some men with strong family histories of baldness keep a full head of hair, and some men with no obvious family history lose theirs early.
Inflammation Plays a Role Too
Male pattern baldness has traditionally been classified as a non-inflammatory type of hair loss, distinguishing it from conditions like alopecia areata where the immune system attacks follicles. But research has complicated that picture. In one study examining scalp biopsies, nearly 88% of samples from men with pattern baldness showed clusters of immune cells around the hair follicles. Inflammation adjacent to miniaturized follicles specifically was observed in over 86% of cases.
Most of this inflammation was mild, concentrated around the upper portions of the follicle rather than deep at the root. It’s not yet clear whether this inflammation helps drive hair loss or is simply a consequence of follicles being damaged by DHT. But the finding suggests that the hormonal and inflammatory pathways may work together, and it helps explain why some men lose hair faster than their genetics alone would predict.
Smoking and Oxidative Stress
Your genes set the stage, but environmental factors can speed up the timeline. Smoking is one of the clearest accelerators. A 2020 study comparing male smokers and nonsmokers between ages 20 and 35 found striking differences: 425 out of 500 smokers showed some degree of hair loss, compared to 200 out of 500 nonsmokers. Among smokers, 47% had reached stage 3 hair loss and 24% had reached stage 4. Only 10% of nonsmokers progressed that far.
The mechanism involves oxidative stress. Tobacco smoke increases your body’s production of free radicals, unstable molecules that damage cells. Toxic chemicals in smoke can harm the DNA of cells in your hair follicles, impairing their ability to grow hair normally. Research has also found that cells in the follicles of balding scalps are particularly sensitive to oxidative stress, which means the follicles already weakened by DHT are the most vulnerable to additional damage from smoking and other environmental sources of free radicals.
How Hair Loss Typically Progresses
Male pattern baldness follows a fairly predictable path, mapped out by the Norwood scale, a seven-stage classification system. In the earliest stage, there’s no noticeable change. Stage 2 typically involves slight recession at the temples, which many men notice in their 20s without it progressing further for years. By stages 3 and 4, the recession deepens and thinning at the crown becomes visible. In the most advanced stage, only a band of hair around the sides and back of the head remains, and even that hair is often fine and sparse.
Not everyone follows the same pattern. A less common variant, called Norwood class A, involves the hairline receding straight back uniformly from front to back without developing a separate bald spot at the crown. The speed of progression also varies widely. Some men go from a full head of hair to significant thinning in five years. Others stay at an early stage for decades.
Treatment Options
Two medications have FDA approval for treating male pattern baldness. Minoxidil is a topical solution available without a prescription. In clinical trials, it has been shown to reduce hair loss, stimulate new growth, and strengthen existing strands. It works best for maintaining what you have and producing modest regrowth, particularly at the crown. You apply it directly to the scalp, typically twice daily, and results take several months to become visible. If you stop using it, any hair you’ve maintained or regrown will gradually be lost.
Finasteride is a prescription pill that works by blocking the enzyme responsible for converting testosterone into DHT. By lowering DHT levels in the scalp, it slows down follicle miniaturization. Studies show it slows further hair loss in about 80% to 90% of men who take it. Like minoxidil, it requires continuous use. Stopping the medication allows DHT levels to rise again and hair loss to resume. Some men use both treatments together for a combined effect, targeting hair loss through two different pathways.