Inhibition of 5α-reductase results in decreased conversion of testosterone to DHT by reducing the Δ4,5 double-bond.
Other enzymes compensate to a degree for the absent conversion, specifically with local expression at the skin of reductive 17β-hydroxysteroid dehydrogenase, and oxidative 3α-hydroxysteroid dehydrogenase and 3β-hydroxysteroid dehydrogenase enzymes [REF].