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Male pattern hair loss comes down to two things: a hormone called DHT and the genes you inherited. In sensitive follicles, DHT slowly shrinks the hair until it stops growing. It runs in families, and most men who lose hair have completely normal testosterone. Lowering DHT is exactly how finasteride slows the process.
Most men assume hair loss means something has gone wrong with their testosterone, or that they did something to cause it. Neither is true. Male pattern baldness, the medical name is androgenetic alopecia, is driven by a hormone your body makes on purpose and a genetic blueprint you had from birth.
Understanding the actual mechanism does two things. It tells you why the hair recedes in the order it does, and it explains why the treatments that work, work. So here is what's really happening on your scalp.
The hormone behind it: DHT
Your body converts a portion of testosterone into a more potent androgen called dihydrotestosterone, or DHT. The enzyme that does the conversion is 5-alpha-reductase. DHT is useful during development and puberty, but in adulthood it has a side effect in certain hair follicles.
In follicles that are genetically sensitive to it, DHT binds to androgen receptors and starts shrinking them. Each hair grows in cycles, and the active growing phase, called anagen, gets a little shorter every cycle. The follicle keeps producing hair, but each new strand comes back finer, shorter, and lighter than the last. This is miniaturization. Repeat it enough times and the follicle eventually goes dormant and stops pushing out a visible hair at all.
That single mechanism is the reason finasteride exists. The drug blocks 5-alpha-reductase, which lowers DHT, which slows the shrinking. Take the pressure off the follicle and the cycle stops accelerating downhill. It's also why early treatment matters more than late treatment: you can preserve a follicle that's still cycling, but you can't easily wake one that's already gone quiet.
Why genetics load the dice
Whether your follicles are sensitive to DHT in the first place is inherited. And this is where one of the most persistent myths needs to go.
Baldness doesn't come from your mother's father. It comes from both sides of your family, through many genes acting together.
— John Venzor, DO
The old "look at your maternal grandfather" rule has a kernel of truth. One important hair-loss gene does sit on the X chromosome, which men get from their mothers. But androgenetic alopecia is polygenic, meaning dozens of genes contribute, and they come from both parents. A father with a full head of hair is no guarantee, and a bald maternal grandfather is no sentence. Your risk is the sum of what both sides handed down, layered on top of age and cumulative DHT exposure over the years.
Here's the part that surprises men most. The vast majority who develop male pattern loss have normal testosterone levels. The problem isn't how much testosterone or DHT you make. It's how sensitive your follicles are to it. Two men with identical hormone levels can have completely different hairlines because of that inherited receptor sensitivity. That distinction is what links the cause to the treatment, and it's covered alongside the early signs to watch for.
Why it follows a predictable pattern
Male pattern loss isn't random thinning. It marches in a recognizable order: the temples recede, the hairline moves back, the crown thins, and the bald areas slowly meet in the middle. The back and sides of the scalp usually hold their hair for life.
That pattern isn't a coincidence. The follicles at the front, top, and crown are the ones genetically programmed to be DHT-sensitive. The follicles along the back and sides, the occipital and temporal fringe, are genetically DHT-resistant. They keep growing normally even while everything above them miniaturizes.
This is also the reason hair transplants work. Surgeons take resistant follicles from the back of the scalp and move them to the thinning zones, where they keep their resistance and continue growing in their new home. The map of where you lose hair is really a map of which follicles inherited sensitivity and which didn't.
Myths worth dropping
A lot of folk explanations for balding have nothing to do with the actual cause. None of the following lead to male pattern hair loss:
- Wearing hats. A hat doesn't suffocate follicles or cut off circulation in any way that thins hair.
- Washing or shampooing often. The hairs you see in the drain were already shed. Frequency of washing has no effect on the genetic process.
- Blow-drying or styling. Heat can damage the hair shaft, but it doesn't miniaturize the follicle the way DHT does.
- "Clogged pores" or poor scalp circulation. These are popular sales pitches for tonics and brushes, not real drivers of androgenetic alopecia.
- Masturbation or frequent sex. Neither raises your DHT enough to matter, and neither causes baldness. This one refuses to die online, and it's still wrong.
Stress and rapid weight changes can trigger a separate kind of shedding called telogen effluvium, which usually recovers on its own. That's worth knowing so you don't confuse a temporary shed with the slow, patterned loss this article is about. If your thinning follows the temple-and-crown pattern and has crept on over years, DHT and genetics are the likely answer, and that's the version with proven treatments.
See a clinician in person if hair loss comes on suddenly, falls out in round patches, or arrives with a scaly, itchy, or scarring scalp. Those patterns point to causes other than androgenetic alopecia and need a different workup.