Section 18. Skin Disorders

Chapter 207. Hair Disorders

Topics: Introduction | Excessive Hairiness | Hair Loss | Ingrown Beard Hairs

Hair Loss

Hair loss (alopecia), most common on the head, may affect any part of the body.

Hair loss may develop gradually or suddenly. It results from hereditary factors, aging, local skin conditions, and diseases that affect the body generally (systemic diseases). Many different drugs can also cause hair loss. When it occurs on the head, hair loss is generally referred to as baldness.

Androgenetic alopecia is the most common type of hair loss, eventually affecting about half of all men (male-pattern baldness) and 10 to 20% of women (female-pattern baldness). A slightly elevated level of the male hormone dihydrotestosterone probably plays a major role, along with genetic factors. The hair loss can begin at any age, even during the teenage years.

In men, hair loss usually begins at the forehead or on the top of the head toward the back. Some men lose only some hair and have only a receding hairline or a small bald spot in the back. Others, especially men whose hair loss began at a young age, lose all of the hair on the top of the head but retain hair on the sides and back of the scalp.

In women, hair loss begins on the top of the head and is usually a thinning of the hair rather than a complete loss of hair. The hairline typically stays intact. This pattern is referred to as female-pattern baldness.

Toxic alopecia is hair loss resulting from physical or psychologic stress. Sudden weight loss, many severe illnesses (particularly those that involve a high fever), or surgery may cause hair loss. Some drugs--including chemotherapy drugs, blood pressure drugs, lithium, valproate, oral contraceptives, vitamin A, and retinoids--can also cause the condition. Toxic alopecia may also result from an underactive thyroid gland or pituitary gland and commonly occurs after pregnancy.

The hair may fall out soon after the disease or condition that is causing the hair loss occurs or as long as 3 or 4 months later. Usually, the hair loss is temporary, and the hair grows back.

Alopecia areata is a common skin disorder in which round, irregular patches of hair are suddenly lost. The cause is believed to be an autoimmune reaction, in which the body's immune defenses mistakenly attack the hair follicles. The site of hair loss is usually the scalp or beard. Rarely, all body hair is lost, a condition called alopecia universalis. Alopecia areata occurs in both sexes and at all ages but is most common in children and young adults. Alopecia areata is not the result of another disease, although some people also have a thyroid disorder. The hair usually grows back in several months. In people with widespread hair loss, regrowth is unlikely.

Hair pulling (trichotillomania) is the habitual pulling out of normal hair. The habit is most common in children but may occur in adults. The hair pulling may not be noticed for a long time, making doctors and parents think that an illness such as alopecia areata or a fungal infection is causing the hair loss.

Scarring alopecia is hair loss that occurs at scarred or damaged areas. The skin may be damaged from burns and other physical injuries or from x-ray therapy. Diseases that cause scarring include lupus erythematosus, lichen planus, and persistent bacterial or fungal infections. Skin cancers also may scar the skin.

Diagnosis and Treatment

A doctor diagnoses male-pattern or female-pattern baldness based on its typical appearance. Determining the cause of other types of hair loss simply by observation is sometimes difficult. A doctor usually examines the hair shafts under a microscope and may perform a biopsy of the skin (see Section 18, Chapter 202). A biopsy helps determine if the hair follicles are normal; if they are not, the biopsy may indicate possible causes. If the doctor's examination finds signs of hormonal irregularities or other serious illness, blood tests to identify those disorders may be needed.

Male-pattern and female-pattern baldness can sometimes be treated effectively with drugs. Minoxidil may stimulate and support hair growth when applied directly to the scalp daily. Finasteride works by blocking the effects of male hormones on the hair follicles and is taken by mouth daily. Improvement may occur with either of these drugs when taken for several months. The most important effect of these drugs may be to prevent further hair loss. The effects last only as long as the drugs are taken.

A more permanent solution is hair transplantation, in which hair follicles are removed from one part of the scalp and transplanted to the bald area. In a newer hair transplantation technique, only one or two hairs are transplanted at a time. Although this technique is more time consuming, it does not require removal of large plugs of skin and allows the implants to be oriented in the same direction as the natural hair.

Toxic alopecia generally resolves after the toxic substance is discontinued. Because the hair loss is usually temporary, wigs often offer the best treatment. A person undergoing chemotherapy should consult a wig maker even before therapy begins so that an appropriate wig can be ready when needed.

Alopecia areata can be treated with corticosteroids. For small bald patches, corticosteroids are typically injected under the skin of the bald patch, and minoxidil may be applied topically as well. For larger patches, corticosteroids are sometimes taken by mouth, but hair often falls out again when treatment is discontinued. Another treatment for alopecia areata involves applying irritating chemicals, such as anthralin, to the scalp to induce a mild allergic reaction or irritation. The irritation sometimes promotes hair growth.

Scarring alopecia is particularly difficult to treat. When possible, the cause of the scarring is treated, but after an area is fully scarred, hair growth is unlikely.