Men go bald primarily because of a hormone called DHT (dihydrotestosterone) that gradually shrinks hair follicles until they can no longer produce visible hair. This process, called androgenetic alopecia or male pattern baldness, affects roughly two-thirds of men by age 35 and about 85% by age 50. It’s overwhelmingly the most common cause of hair loss in men, and it comes down to a combination of genetics, hormones, and time.
How DHT Shrinks Hair Follicles
Testosterone circulates through every man’s body, but a small portion of it gets converted into a more potent hormone called DHT. On its own, DHT isn’t a problem. It plays a role in male development during puberty and helps maintain certain masculine traits. The trouble starts when DHT binds to receptors on hair follicles across the scalp.
When DHT latches onto a follicle’s receptor, it triggers a process called miniaturization. The follicle gradually produces thinner, shorter, lighter hairs with each growth cycle. A strand that once grew thick and dark for several years might only grow for a few months and come in nearly invisible. Eventually, the follicle shrinks so much it stops producing hair altogether. This is why balding areas often look thin and wispy before they go completely bare.
What makes this puzzling is that DHT doesn’t affect all follicles equally. The hair on the sides and back of the head is largely resistant to DHT, which is why even men with advanced baldness keep that horseshoe-shaped ring of hair. The follicles on top of the scalp and around the temples are genetically programmed to be vulnerable.
Why Genetics Matter More Than Anything Else
The single most confirmed genetic factor in male baldness is the AR gene, which provides instructions for building androgen receptors. Variations in this gene can make your androgen receptors more sensitive to DHT than normal. In other words, two men can have identical DHT levels, but the one with more reactive receptors will lose hair faster because his follicles overrespond to the hormone.
The AR gene sits on the X chromosome, which men inherit from their mothers. This is where the old advice to “look at your mother’s father” comes from. There’s truth to it, but it’s incomplete. Researchers suspect that variants in several other genes also contribute to baldness, and those can come from either parent. Having a close relative on any side of the family with pattern hair loss increases your risk. The inheritance pattern is complex enough that predicting exactly who will go bald, and how severely, remains difficult.
The Typical Pattern of Hair Loss
Male pattern baldness follows a fairly predictable path, which doctors measure on a seven-stage scale. In the earliest stage, the hairline recedes slightly around the temples, forming what’s sometimes called a “mature hairline.” Many men settle here and never progress further.
For those who do progress, the next stage brings the first signs of clinically significant thinning, either at the temples or on the crown. Over time, these two thinning zones expand and merge. In moderate stages, a band of hair still connects the front to the sides, but this bridge narrows. In the most advanced stages, only a band of hair around the sides and back of the head remains, and even that hair can be fine and sparse.
Not every man follows this sequence exactly. Some lose hair primarily at the crown while keeping a relatively intact hairline. Others see their hairline retreat dramatically while the crown stays full for years. The speed varies too. Some men notice significant thinning in their early twenties, while others don’t see major changes until their fifties or later.
Smoking and Other Accelerating Factors
Genetics loads the gun, but certain habits can pull the trigger faster. Smoking is the best-studied environmental factor. A large community survey of Asian men found that those who smoked 20 or more cigarettes per day were more than twice as likely to have moderate or severe baldness compared to nonsmokers, even after accounting for age and family history. The proposed mechanisms include damage to the tiny blood vessels feeding hair follicles, DNA damage from smoke toxins, oxidative stress that triggers inflammation around follicles, and hormonal shifts that may reduce the protective effects of estrogen on hair.
Chronic stress, poor nutrition, and certain medical conditions can also accelerate hair loss, though these tend to cause a more diffuse thinning pattern rather than the classic receding-and-crown pattern driven by DHT. Severe calorie restriction, iron deficiency, and thyroid problems are common culprits behind sudden or widespread shedding that gets mistaken for male pattern baldness.
Do Hats Cause Baldness?
No. Studies of identical twins found that men who wore hats daily actually experienced less hair loss at the temples than their non-hat-wearing twins. The concern that hats restrict blood flow to follicles is theoretically possible only with extremely tight or heat-trapping headwear, and even then, any resulting hair loss would start as temporary. What can cause real damage is pulling hair into tight styles underneath a hat. That chronic tension on follicles, called traction alopecia, is caused by the hairstyle rather than the hat itself.
How Current Treatments Work
The two main approaches to slowing or partially reversing male pattern baldness target different parts of the problem. One approach blocks the enzyme that converts testosterone into DHT, reducing DHT levels throughout the body. Less DHT means less follicle shrinkage, and some men see partial regrowth of miniaturized hairs.
The other approach, a topical treatment applied directly to the scalp, works by pushing resting follicles back into their active growth phase prematurely and extending how long that growth phase lasts. It also appears to increase the physical size of shrunken follicles. This treatment doesn’t address DHT at all, which is why the two approaches are often used together.
Both treatments work best when started early, before follicles have fully shut down. A miniaturized follicle that still produces fine, thin hair can often be coaxed back to producing thicker strands. A follicle that has been dormant for years is much harder to revive. This is why men who start treatment at the first signs of thinning tend to see better results than those who wait until baldness is well established. Both options require ongoing use to maintain results, since the underlying genetic sensitivity to DHT never goes away.
Why Some Follicles Are Vulnerable and Others Aren’t
One of the most fascinating aspects of male baldness is the geographic specificity. The follicles on top of your head and the ones on the sides are genetically different from each other, even though they look identical. Follicles in the balding zone express androgen receptors at higher levels, making them more responsive to DHT. Follicles on the sides and back have lower receptor activity and are largely unaffected.
This difference is so reliable that hair transplant surgery depends on it. Follicles taken from the resistant zone on the back of the head continue to resist DHT even after being moved to the top of the scalp. They carry their genetic programming with them, which is why transplanted hair tends to be permanent while the native hair around it may continue to thin.