Dihydrotestosterone (DHT) is a hormone naturally produced by the human body. It is a metabolite of testosterone, which is converted into dihydrotestosterone by the enzyme 5-alpha-reductase and has the chemical formula C19H30O2. It is an androgen, meaning that it is one of the hormones responsible for the physical development and sexual differentiation of males. DHT bonds to androgen receptors much more effectively than testosterone or other natural androgens, making it a very important member of that group that is essential to normal male sexual development. Most dihydrotestosterone production occurs in the prostate, testes, adrenal gland, and hair follicles.
Dihydrotestosterone's role begins in the womb. A male fetus's body begins producing large quantities of androgens, including DHT, about two months into the pregnancy. These hormones guide the development of the fetus, causing the growth of the penis and scrotum, as well as internal structures such as the vas deferens. A male fetus that does not produce or absorb dihydrotestosterone at normal levels may not develop typically, resulting in various disorders of sexual development.
A condition that prevents the conversion of testosterone into dihydrotestosterone, called 5-alpha-reductase deficiency, causes the child to be born with ambiguous genitalia that may include both male and female organs. Androgen insensitivity syndrome, which is caused by the partial or total inability to metabolize male sex hormones, can also result in ambiguous genitalia. A genetically male child with complete androgen insensitivity syndrome can be born with what appear to be typical female genitalia, though the uterus and internal reproductive organs are absent. Unusually high levels of DHT in a female fetus can also result in the development of ambiguous genitalia.
Increases in dihydrotestosterone levels are also important for male sexual development at puberty, promoting the further development of the sex organs. It is also responsible for many male secondary sexual characteristics, such as increased amounts of facial and body hair and deepening of the voice. The only major male secondary sexual trait in which DHT does not play an important part is the growth of the skeletal muscles, where 5-alpha-reductase is absent. DHT also interferes with the production and effects of the hormone estrogen, thereby discouraging the development of female traits.
Treatments to affect dihydrotestosterone levels are used in medicine. The damaging effects of high levels of DHT on hair follicles is the main cause of male pattern baldness, and excess DHT can also cause enlargement of the prostate and lead to the development of prostate cancer. The drug finasteride, used in the treatment of both enlarged prostate and male pattern baldness, works by inhibiting 5-alpha reductase and thereby decreasing the synthesis of DHT.