Male-pattern baldness

Alternative names:

alopecia in men; androgenic alopecia in men; baldness - male; hair loss in men

Definition:

A typical pattern of loss of hair in men, caused by hormones and genetic predisposition.

Causes, incidence, and risk factors:

Scalp hair grows from the hair follicle at an average rate of 1/2 inch per month. Each hair grows for 4 to 7 years, then rests, and finally falls out. A new hair then begins growing in its place. At any one time, about 85% of the hair is growing and 15% is resting.

Baldness occurs when there is a progressive miniaturization of the follicle resulting in shorter and finer hair. The end result is a miniature follicle with no hair. The cause of the failure to grow a new hair is not well understood, but it is associated with a genetic predisposition and the presence of endocrine hormones (androgens), especially testosterone. The follicle, however, remains alive, suggesting the possibility of new growth.

The typical pattern of male-pattern baldness begins at the hairline. The hairline gradually recedes to form an "M" shape. The existing hair may be finer and does not grow as long as when younger. The hair at the crown also begins to thin, and eventually the top points of the hairline "M" meet the thinned crown, leaving a horseshoe pattern of hair around the sides of the head.

Hair loss in patches, diffuse shedding of hair, breaking of hair shafts, or hair loss associated with redness, scaling, pain, or rapid progression would usually be associated with other causes.