Hair loss and Hormones

Hair loss and Hormones

Hormones are biochemical substances that are made in various glands throughout the body. These glands secrete their products directly into the bloodstream so that the chemical they make is spread throughout the body. These chemicals are very powerful so that only minute amounts of them have profound effects upon the body.

The major male sex hormone is called testosterone. Testosterone and other related hormones that have masculinizing effects are made primarily in the testicles; therefore, the hormonal levels that are seen in adults do not reached significant levels until the testicles develop and enlarge during puberty. In fact, these same hormones are the cause of many of the changes that occur in puberty; growth of phallus and scrotum, sperm production, development of a sex drive, change in the voice, growth of axillary and pubic hair, development of an adult aroma in the sweat, increase in bone and muscle mass, and change in the basic body shape.

These same hormones that cause acne and beard growth can also signal the beginning of baldness. The presence of androgens; testosterone, and its related hormone DHT, cause some follicles to regress and die. In addition to the testicles, the adrenal glands located above each of our kidneys, produce androgenic hormones, and this would be similar in both sexes. In females, the ovaries are an additional source of hormones that can affect hair.

The specific relationship between testosterone and hormonally induced hair loss in men was discovered by a psychiatrist early in this century. At that time, castration was commonly performed on patients with certain types of mental illness as it seemed to have a calming effect upon many patients and castration reduced the sex drive of patients who had no outlet for their desires. The doctor noted that the identical twin brother of one patient was bald while the mentally ill (castrated) twin had a full head of hair. The doctor decided to determine the effect of treating his patient with testosterone, which had recently become available in a purified form. He injected the hairy twin with testosterone to see what would happen. Within weeks, the hairy twin began to lose all but his wreath of permanent hair, just like his normal twin. The doctor, then, stopped giving the testosterone to see whether the process would be reversed, but the balding process continued and his patient never regained his full head of hair. It was apparent to him that eliminating testosterone will slow, or stop, further hair loss once it has begun, but it will not revive any dead follicles.

The hormone felt to be directly involved in androgenetic alopecia is actually dihydrotestosterone (DHT) rather than testosterone. DHT is formed by the action of the enzyme 5-a reductase on testosterone. DHT acts by binding to special receptor sites on the cells of the hair follicles to cause the specific changes associated with balding.

In men, 5-a reductase activity is higher in the balding area. This helps to explain the reason for the patterned alopecia that males experience. The enzyme 5-a reductase is inhibited by the hair loss medication finasteride (Propecia).

DHT decreases the length of the anagen (growing) cycle, and increases the telogen (resting) phase, so that with each new cycle the hair shaft becomes progressively smaller. In addition, DHT causes the bitemporal reshaping of hairline seen as adolescents enter adulthood, as well as patterned baldness (androgenetic alopecia). DHT also causes prostate enlargement in older men and adolescent and adult acne.

It is interesting that testosterone effects axillary and pubic hair, whereas DHT effects beard growth, hair on trunk and limbs, patterned baldness and the appearance of hair in the nose and ears (something that older men experience). Scalp hair growth, however, is not androgen dependent, only scalp hair loss depends on androgens.