Loss of part or all of the hair, most commonly the hair on the scalp
Alopecia, or hair loss, can occur in any body area but is particularly noticeable when it affects the scalp. The condition may be localized, in which hair is lost in patches, or generalized, in which there is thinning or total hair loss over the whole scalp. Hair loss can be temporary or permanent. Alopecia is not always associated with ill health, but it may cause embarrassment.
The most common cause of alopecia in men is oversensitivity to the hormone testosterone, producing a characteristic pattern of hair loss (see Male-pattern baldness).
Patchy hair loss is usually due to alopecia areata, an autoimmune disorder that causes bald patches to appear on the scalp. These bald areas are surrounded by short, broken hairs. The hair usually regrows within 6 months, but in rare cases alopecia areata can cause permanent loss of all body hair.
Hairstyles that pull on the scalp are a common cause of patchy hair loss; if the pulling is continuous, hair loss may be permanent. Patchy hair loss may be the result of a rare psychological disorder in which the hair is compulsively pulled. Burns or skin disorders, such as ringworm, which scar the scalp may cause patchy hair loss.
Generalized hair loss is normal in elderly people. It may also occur temporarily after pregnancy and is a common side effect of chemotherapy. Other causes of thinning hair include acute illness, stress, and malnutrition.
Your doctor will probably be able to diagnose alopecia areata by the appearance of your scalp. This condition does not usually require treatment, but corticosteroids injected into the hairless patches may be effective in promoting regrowth. In most other cases of hair loss, the hair usually regrows once the underlying cause has been treated. Hair lost during pregnancy usually regrows about 3 months after childbirth.
If your scalp has patchy scarring, you may need a skin biopsy to diagnose the underlying cause. Scarred areas may be treated with topical corticosteroids or antifungal drugs, but if the damage is severe and has affected the hair follicles it is unlikely that new hair will grow.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.