Alopecia areata (patchy baldness) is a relatively common, non-contagious autoimmune disease that causes hair loss. It can occur on the scalp or other parts of the body in both men and women.

The cause of alopecia areata is unknown.  It typically occurs first in childhood, and appears as one or more round bald patches on the scalp approximately the size of a quarter. The patches typically occur suddenly.

In most instances, alopecia areata does not progress beyond a few bald patches. However, complete baldness of the head (alopecia areata totalis) or complete hair loss on the head, face and body (alopecia areata universalis) may occur in very rare cases. Some individuals may also develop "pits" or "dents" in the fingernails as a result of the disease.

Each person sheds and regrows hair daily. Hair loss results when more hairs are being shed than regrown. Unlike animals, humans have a distinct pattern of growing, resting and shedding hair. Humans have a distinct number of terminal hair follicles at birth. These follicles grow and shed hairs in cycles.

During the normal cycle of hair growth, approximately 90 percent of the hair on a person’s scalp is growing at any one time. This growth (anagen) phase may last several years, with each hair growing about one centimeter per month during this time. When hair stops growing, it enters a resting (telogen) phase of three to four months. Hair is released from the hair shaft and shed from the scalp, initiating the next cycle of growth. Each day about 75 hairs are lost from a healthy person’s head.

The National Institutes of Health (NIH) estimates that alopecia areata affects approximately 4 million Americans at some point in their lives. Instances of the disease are commonly noted in people of both genders and of all ages and ethnic backgrounds. Alopecia areata is not painful or life-threatening and patients are often generally healthy otherwise.

Alopecia areata generally occurs in two forms:

• A mild form where less than 50 percent of scalp hair is lost
  
  
• An extensive form where greater than 50 percent of scalp hair is lost

The majority of patients with alopecia areata have the more mild form of the disease. Treatment results tend to be less effective for patients with extensive hair loss.