Why do men lose their hair?

An excess of hormones may be one key to the mystery of male baldness.

The problem begins in the oily sebaceous glands, which are adjacent to hair follicles throughout the body except on the palms of the hands and the soles of the feet. The sebaceous glands in the skin of bald scalps collects an abundance of male hormones, researchers at the University of Miami School of Medicine have discovered. These hormones, which are known as androgens, then short-circuit normal hair growth.

The result is male pattern baldness, a condition that afflicts about four in every 10 men between 18 and 39, according to the Society for Investigative Dermatology. In older men, the condition is even more prevalent, affecting about nine out of every 10 men 80 and older.

At the society's annual meeting last month, Dr. Lawrence S. Honig said that specially programmed areas on these glands, known as receptors, selectively collect and store androgens.

Once the receptors collect these androgens, they are moved inside hair follicle cells, where they interfere with hair growth, Honig reported with his colleagues Dr. Marty Sawaya, Dr. Larry Garland and researcher S.L. Hsia.

Normally, hair grows for two to six years, then rests for three months, before falling out. New hairs then grow from the same roots.

But in male pattern baldness, the excess hormones interfere with this normal cycle, researchers believe. The period of hair growth gradually shortens, until hair fails to grow very long. Eventually, some of the roots become inactive, leading to baldness.

Although baldness experts have theorized about hormones interfering with hair growth, this is the first study to show how hormones exert their effects. Experiments were performed on small scalp samples taken from 12 men with male pattern baldness, who ranged in age from 25 to 39. These samples were compared with a control group of 12 men, age 30 to 47 years, with normal hairy scalps.