5-Alpha-Reductase
The enzyme that turns testosterone into the hormone wrecking your hairline.
Grounded in the research on 5α-Reductase (Wikipedia)
Know what it actually does
5-alpha-reductase (5AR) is an enzyme that converts testosterone into dihydrotestosterone (DHT) by reducing a double bond using NADPH. DHT is roughly 3-5x more potent at the androgen receptor than testosterone. So this one enzyme is the bottleneck that decides how much of your T becomes the strongest natural androgen in your body.
Learn the three isozymes
There are three types. Type 1 (SRD5A1): skin, scalp sebaceous glands, liver. Type 2 (SRD5A2): prostate, hair follicles, genital skin, the main driver of male-pattern baldness and prostate growth. Type 3 (SRD5A3): broadly expressed, also glycosylates proteins. Finasteride hits mostly type 2; dutasteride hits type 1 and 2 both.