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RO DHT is not the problem; sensitivity to it is. Dihydrotestosterone is a normal androgen present in everyone. Most men losing hair have entirely ordinary levels of it. What differs between a scalp that keeps its hair and one that does not is how the follicles there respond.
It is made locally, from testosterone. The enzyme 5-alpha-reductase converts testosterone into DHT, which binds the androgen receptor far more tightly than testosterone does. The type 2 form of that enzyme is the one that matters in pattern loss, and it sits in the outer root sheath of the follicle itself (Ho, Sood & Zito, Androgenetic Alopecia, StatPearls). The reaction happens in the skin, not somewhere else in the body.
Sensitivity is regional, and that is what makes surgery possible. Follicles on the top of the head can be susceptible while those at the back and sides are not, on the same person, with the same hormone reaching both. A follicle keeps that programming when it is moved — the principle called donor dominance.
Nothing about surgery changes the hormone. Transplanted hair is placed among native hairs that remain susceptible, and those continue to respond. This is why medical treatment and surgery answer two different halves of the same problem.
Related terms
For the medication that acts on this enzyme, see our finasteride paper. For whether it should be continued after surgery, see finasteride after a hair transplant.
