SRD5A2, or 5-alpha-reductase 2, is an enzyme that facilitates the conversion of testosterone into dihydrotestosterone (DHT), a more potent androgen. It is mainly expressed in androgen-sensitive tissues such as the prostate gland, hair follicles, and external genitalia. SRD5A2 plays a key role in androgen metabolism and the regulation of androgen signaling. Testosterone, produced primarily in the testes, adrenal glands, and ovaries, acts as the precursor for DHT. By reducing the 4,5 double bond in the A ring of testosterone, SRD5A2 increases the binding affinity of DHT to the androgen receptor (AR).