Definition of Male pattern baldness:

Male pattern baldness is the most common type of hair loss in men. It usually follows a typical pattern of receding hairline and hair thinning on the crown, and is caused by hormones and genetic predisposition.

Causes, incidence, and risk factors:

Hair grows about an inch every couple of months. Each hair grows for 2 to 6 years, remains at that length for a short period, then falls out. A new hair soon begins growing in its place. At any one time, about 85% of the hair on your head is in the growing phase and 15% is not.

Each hair sits in a cavity in the skin called a follicle. Baldness in men occurs when the follicle shrinks over time, resulting in shorter and finer hair. The end result is a very small follicle with no hair inside. Ordinarily, hair should grow back. However, in men who are balding, the follicle fails to grow a new hair. Why this occurs is not well understood, but it is related to your genes and male sex hormones. Even though the follicles are small, they remain alive, suggesting the possibility of new growth.