DHT (Dihydrotestosterone)

DHT is the main androgen acting on susceptible scalp follicles in pattern hair loss. Chemically it differs from testosterone by a single saturated bond and is roughly 2 to 3 times more potent at the androgen receptor.

The body makes DHT locally inside tissues that express the enzyme 5α-reductase, including the scalp, prostate, sebaceous glands, beard, body hair, and genitals. Lowering DHT in the scalp (with a 5α-reductase inhibitor like finasteride or dutasteride) is the most evidence-based way to halt and partly reverse pattern hair loss.

DHT is not relevant to telogen effluvium, alopecia areata, or scarring alopecias. It only matters for androgen-driven loss.