Alopecia Health Article

Definition

Alopecia is the partial or complete loss of hair—especially on the scalp—either in patches (alopecia areata), on the entire head (alopecia totalis), or over the entire body (alopecia universalis).

Description

A basic understanding of hair biology and normal hair development is essential in distinguishing normal versus abnormal hair loss in children and adolescents.

Hair consists of the shaft and the root, which is anchored into a follicle beneath the epidermis. Hair is formed by rapid divisions of cells at the base of the follicle. Except for a few growing cells at the base of the root, hair, which is composed of keratin and other proteins, is dead tissue.

An individual hair follicle has a long growth phase, producing steadily growing hair for two to six years. About 80 percent to 90 percent of hair follicles are involved in this active growing period called the anagen phase. Next is a brief transitional phase (of about three weeks' duration)—the catagen phase—during which the hair follicle degenerates. About 5 percent of follicles are involved in the catagen phase.

Then a dormant period known as the telogen phase occurs. About 10 percent to 15 percent of hairs are involved in this phase, which lasts for approximately three months. Following the telogen phase, the growth phase begins again, and the growth cycle repeats.

Each person has about 100,000 hairs on their scalp. Although it is normal to lose between 25 and 100 hairs per day, any disruption of the hair growth cycle may cause abnormal hair loss.

Demographics

It is estimated that alopecia affects several million children in the United States and that hair loss is responsible for about 3 percent of all pediatric office visits.

Alopecia areata affects both sexes and all ages but is most common in children five to 12 years old. About one per 1000 children has alopecia areata. Approximately 5 percent of children with alopecia areata go on to develop alopecia totalis, and some of these children may develop alopecia universalis.

Tinea capitis (ringworm) affects an estimated 10 percent to 20 percent of susceptible children, and although the demographics are sketchy, telogen effluvium is the most common type of alopecia in both children and adults.

Causes and symptoms

Although in children and adolescents, hair loss may be caused by a wide variety of factors, most children experience hair loss as a result of one of four major causes:

• fungal infections
• alopecia areata
• trauma to the hair shaft
• telogen effluvium

A fungal infection called tinea capitis, which is similar to athlete's foot, is a common cause of hair loss, particularly among toddlers and early school-aged children. Tinea capitis, which affects the hair root, is a highly contagious condition and is often transmitted when a child uses the comb, brush, hat, or bed linen of an infected child. Tinea capitis seldom occurs after puberty.

Children with this condition usually have patchy hair loss with some broken hairs visible just above the surface of the scalp. The patches of hair loss are usually round or oval but are sometimes irregular in shape. When broken off at the surface, the hairs resemble small black dots on the scalp. Occasionally gray flakes or scales are present.

Alopecia areata, or localized baldness, is the sudden appearance of sharply defined circular or oval patches of hair loss, most often on the scalp. These patches are smooth and without inflammation, scaling, or broken hairs and may appear overnight or over the course of a few days. This condition may affect scalp hair, the eyebrows, eyelashes, genital area, and occasionally the underarms. The hair loss is not accompanied by other visible evidence of scalp disease, and the condition is not contagious.

In alopecia areata, immune system cells (white blood cells) attack the rapidly growing cells in the hair follicles that produce hair. The affected hair follicles decrease in size and hair production slows drastically. Because the stem cells that continually supply the follicles with new cells do not appear to be affected, the follicle retains the potential to regrow hair.

Although it is uncertain why the hair follicles undergo these changes, it is thought that a combination of genes may predispose some children and adults to the disease. In those who are genetically predisposed, some type of trigger—perhaps a virus or something in the child's environment—brings on the attack against the hair follicles.

Trauma to the hair shaft is another common cause of hair loss in children. Often the trauma is caused by traction resulting from, for example, tight braids, ponytails, or by friction (hats, hair bands, or rubbing against a bed). Trauma may also be caused by chemicals or burns.

Another important cause of hair trauma is called trichotillomania—a habit similar to thumb-sucking or nail-biting—of twirling or pulling out the hair. Trichotillomania is generally considered to be a nervous habit and may include the pulling of eyebrows and eyelashes.

The hair loss associated with trichotillomania is patchy and is characterized by broken hairs of varying length. Within the patches, hair loss is not complete. If the hair trauma is not severe or chronic enough to cause scarring, the child's hair usually regrows when the trauma ceases.

Telogen effluvium, another common cause of hair loss, affects both children and adults. This condition is responsible for more hair loss than any other cause except adult male-pattern baldness. In telogen effluvium, there is a physiologic basis to the hair loss; something happens to interrupt the hair's normal growth cycle and to drive many or all of the hairs into the telogen phase. Between six and 16 weeks later, partial or complete baldness occurs.

Many factors can cause telogen effluvium, including the following:

• high fever
• medications, including chemotherapy
• crash diets
• excessive vitamin A
• emotional stress
• surgery
• severe injury

In the telogen phase, a child's hair undergoes growth spurts and pauses. During the rest phase between spurts, the bulb at the end of the hair root decreases in volume and the hair loosens. Although exaggerated during adolescence, particularly in girls (due the influence of female hormones), even preadolescents may experience excessive hair loss on a daily basis. The scalp hair, however, appears normal in this condition.