How DHT miniaturizes a susceptible follicle
Male pattern baldness, or androgenetic alopecia, arises from the interaction of genetic susceptibility with dihydrotestosterone (DHT), a potent androgen produced from testosterone by the enzyme 5-alpha-reductase. In genetically sensitive scalp follicles, DHT progressively shortens the active growth phase of the hair cycle and shrinks the follicle. Over successive cycles thick terminal hairs are replaced by finer, shorter ones in a process called miniaturization, until the follicle produces little visible hair.
The pattern is characteristic because follicles in different scalp regions carry different sensitivity. Hair at the temples and crown is typically most susceptible, while the back and sides are often spared, which is the basis for hair transplantation.
Why progression varies so much between men
Susceptibility is polygenic and inherited from both sides of the family, so onset, speed, and final extent vary widely. Because the driver is an ongoing hormonal process, the condition is generally progressive without intervention, and any benefit from treatments that block DHT or prolong the growth phase tends to fade if treatment stops.
This is general educational information, not medical advice. Hair-loss treatments have specific risks and limits and should be discussed with a clinician.