Baldness, or alopecia, is total or partial loss of scalp hair. The condition may be temporary or permanent. The most common
type of alopecia is pattern baldness, a hereditary trait that is expressed more often in males than in females because it depends on the influence of the male hormone testosterone. Pattern baldness in males extends until only a sparse growth of hair remains on the back and sides of the head. In women, the baldness usually extends until only a sparse growth remains on the crown. Neither hair tonics nor any other medical measure can prevent or reverse such baldness.
Premature baldness may partly result from an imbalance of sex hormones. Sudden
temporary hair loss sometimes occurs as a result of typhoid fever, influenza, pneumonia, or stress. Gradual thinning of the hair may be caused by severe nutritional deficiency, tuberculosis, cancer, and disorders of the thyroid gland or pituitary gland. Temporary baldness also may be caused by exposure to nuclear radiation or X rays or by the internal use of certain anticancer drugs. Plugs of hair-containing skin from the back of a bald person's head are sometimes successfully
transplanted on bare areas of the scalp; more painstakingly, individual hair follicles may be transplanted. The hypertension drug minoxidil has been found to restore hair growth. Although originally not approved for such use because of concern over serious side effects, it was approved for sale as a hair restorer (Rogaine) in Canada in 1986 and the United States in 1987. It is expensive, must be used daily, and seems to work mainly on young men who only recently began to lose hair. A second drug, finasteride (Propecia), was approved in 1998 for use by men to treat baldness. Like minoxidil, it must be used daily, and the baldness will return if the drug is stopped. In addition, finasteride has some notable side effects, including impotence.