Hormonal influences on hair

Hormones are very powerful biochemical substances produced by various glands throughout the body. The primary male sex hormone is testosterone. Testosterone and other related hormones that have “masculinizing” effects are produced primarily in the testicles. These same hormones are the cause of many changes that occur in puberty in boys.

The hormones that cause acne and beard growth also can trigger the beginning of baldness. Testosterone is also produced in women from the adrenal glands and the ovaries, and it is produced in lower concentrations than the testicles produce the hormone in men. In women, most of the testosterone is converted into estrogen.

The hormone believed to be most directly involved in androgenetic alopecia is dihydrotestosterone (DHT). DHT is formed by the action of the enzyme 5-alpha reductase (5AR) on testosterone, and it binds to special receptor sites on the cells of hair follicles to cause the specific changes associated with balding.

The presence of androgens (steroid like substances), testosterone (considered an androgen), and DHT cause some hair follicles to regress and die. In addition to the testicles, the adrenal glands located above the kidneys produce androgenetic hormones; this is true for both sexes. In females, ovaries are the major source of hormones that can affect hair.

Androgenetic hormones stimulate many of the male sex characteristics we see in adult men. Androgens like testosterone, are converted into estrogens in women, which make women develop their typical female sex characteristics.

Early in the 20th century, a psychiatrist discovered the specific relationship between testosterone and hormone-induced hair loss. The doctor noted that the identical twin brother of one patient was profoundly bald while the mentally ill twin had a full head of hair. The doctor decided to determine the effect of treating his patient with testosterone, and injected him (the hairy twin) with the hormone. Within weeks, the hairy patient began to lose all but his wreath of permanent hair, just like his twin. The doctor stopped administering testosterone, but his patient never regained his head of hair.