What is Dihydrotestosterone, Free?
Dihydrotestosterone is the 5-alpha-reduced metabolite of testosterone and the most potent endogenous androgen, binding the androgen receptor with roughly two- to threefold greater affinity and dissociating more slowly than its precursor. It is generated largely in peripheral target tissues — skin, hair follicle, prostate, genital tissue — by the type 1 and type 2 isoforms of 5-alpha-reductase, so circulating concentrations partly reflect tissue conversion rather than gonadal secretion alone. In plasma the bulk of DHT travels bound to sex hormone-binding globulin and albumin; only the small unbound fraction is immediately available to diffuse into cells and engage the receptor. Equilibrium dialysis physically separates that free fraction before quantitation, which is why the measured free concentration tracks biological availability more closely than a total value does.