Dihydrotestosterone — DHT — is the molecule that drives male pattern baldness in genetically susceptible men. Understanding what it does explains why finasteride works, why some follicles resist it, and why donor hair from the back of your head lasts forever.
Testosterone is the primary male sex hormone, produced mostly in the testes. The enzyme 5-alpha-reductase converts a portion of circulating testosterone into dihydrotestosterone (DHT) — a more potent androgen that binds to androgen receptors with three to ten times the affinity of testosterone itself.
DHT is essential during fetal development and puberty. In adults, it continues to drive secondary sexual characteristics — body hair, deeper voice, prostate maturation. It's also responsible for male pattern hair loss in men whose scalp follicles have inherited DHT sensitivity.
When DHT binds to receptors on a susceptible follicle, it triggers a cascade that progressively shortens the follicle's growth cycle and miniaturises the hair shaft. Each successive growth cycle produces a thinner, shorter, less pigmented hair — until the follicle stops producing visible hair entirely.
Not every scalp follicle is DHT-sensitive. The follicles at the back and sides of the head — the “donor area” in hair restoration — have inherited a genetic profile that makes them resistant to DHT. They produce normal hair throughout life regardless of how much DHT is present.
This resistance is intrinsic to the follicle itself, not the location. When DHT-resistant donor follicles are transplanted to the front or crown — areas where the original follicles were susceptible — the transplanted follicles retain their resistance. They grow for life in their new location.
This is why hair transplant results are permanent. The transplanted hair isn't fighting against DHT; it's biologically immune to it.
Finasteride inhibits 5-alpha-reductase — the enzyme that converts testosterone into DHT. The result is a roughly 70% drop in scalp DHT levels at standard 1mg daily dosing.
Lower DHT means slower miniaturisation of susceptible follicles. The hair you have now stays longer; the loss progression slows or stops. In about two-thirds of men, finasteride produces measurable hair regrowth or thickening over five years; in another quarter, it stops further loss without regrowth.
Finasteride doesn't make follicles DHT-resistant — that's a genetic property. It just reduces the amount of DHT around them. That's why finasteride needs to be taken continuously: stop the medication, DHT levels return, and miniaturisation resumes where it left off.
For surgical patients, finasteride is the maintenance therapy that preserves the surrounding native hair. The transplanted hair will grow regardless; the native hair around it needs the protection.
Whether finasteride, surgery, or both is the right answer depends on your stage, your goals, and your tolerance for ongoing medication. Send photos for an honest assessment.