What is 5-alpha-reductase and what does it do?
Two 5-alpha-reductase (5aR) iso-enzymes have been identified: type 1 5-alpha-reductase, and type 2 5-alpha-reductase.
Type 1 5aR has been found in various parts of the body including sebaceous glands, the epidermis, sweat glands, nervous system cells and in hair follicles (dermal papilla, outer root sheath, and matrix). In skin, type 1 5aR activity is primarily concentrated in sebaceous glands of the face and scalp. It is also found in the liver, adrenals and kidneys.
Type 2 5aR has been found in hair follicles as well (dermal papilla, the inner and outer sheath, sebaceous ducts and proximal inner root sheath), the prostate, testicles and liver.
Both types of 5aR can combine with testosterone to form the potent male hormone dihydrotestosterone (DHT), which has a strong affinity for androgen receptors and is responsible for triggering the miniaturization of hair follicles in the scalp that leads to hair loss. At this time it is not known how much circulating (in the blood) vs. locally produced (in the cells) DHT contribute to hair loss, relative to each other. Propecia is the only FDA approved drug that combats hair loss by attempting to inhibit the formation of DHT by binding with 5aR.
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