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Alopecia is the loss of hair on the head or on any other part of the body.
Hair loss that occurs on the head is generally called baldness. Hair loss is often of great concern to people for cosmetic reasons, but it can also be a sign of a body-wide (systemic) illness.
Causes
Hair grows in cycles. Each cycle consists of a long growing phase (anagen), a brief transitional phase (catagen), and a short resting phase (telogen). At the end of the resting phase, the hair falls out, and the cycle begins again as a new hair starts growing in the follicle. Normally, about 100 scalp hairs reach the end of resting phase each day and fall out. When many more than 100 hairs per day go into resting phase, hair loss (telogen effluvium) may occur. A disruption of the growing phase causing loss of hairs is called anagen effluvium.
The most common cause of hair loss is
Other common causes of hair loss are
Other factors include heredity, aging, and local skin conditions.
Androgenetic Alopecia:
This form of alopecia eventually affects about half of all men (male-pattern hair loss) and women (female-pattern hair loss). The hormone dihydrotestosterone plays a major role, along with heredity. 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 begins 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. This pattern is referred to as male-pattern hair loss.
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 hair loss.
Anagen Effluvium:
Anagen effluvium is hair loss caused by exposure to drugs or other chemicals that disrupt the growing phase (anagen) of hair. Examples include chemotherapy drugs, certain poisons (such as boric acid, mercury, and thallium), and radiation.
Telogen Effluvium:
Telogen effluvium is hair loss caused by physical or psychologic stress that increases the number of hairs that go into resting phase (telogen). Sudden weight loss, severe illness (particularly one that involves a high fever), or surgery may cause hair loss. Some drugs—including chemotherapy drugs, blood pressure drugs, lithium, anticonvulsants, oral contraceptives, anticoagulants, ACE inhibitors, vitamin A, and retinoids—can also cause the condition. Telogen effluvium may also result from an underactive or overactive thyroid gland or pituitary gland and commonly occurs after pregnancy and menopause.
The hair typically falls out 3 or 4 months after the event that caused the stress. Usually, the hair loss is temporary, and the hair grows back.
Alopecia Areata:
In this common skin disorder, round, irregular patches of hair are suddenly lost. The margins of the patches have characteristic short, broken hairs, which resemble exclamation points. The cause is believed to be an autoimmune reaction in which the body's immune defenses mistakenly attack the hair follicles. Alopecia areata is not the result of another disease, but some people may also have a thyroid disorder or vitiligo (a skin pigment disorder).
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. The hair usually grows back in several months. In people with widespread hair loss, regrowth is less likely.
Hair Pulling (Trichotillomania):
This disorder 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, causing confusion for doctors and parents who mistakenly think that an illness such as alopecia areata or a fungal infection is causing the hair loss.
Traction Alopecia:
This disorder is hair loss caused by tight braids, rollers or ponytails that pull constantly on hair. Hair loss most often occurs at the hairline of the forehead and temples.
Scarring Alopecia:
Scarring alopecia is the result of destruction of the hair follicle causing it to be replaced by scar tissue. Diseases that cause scarring alopecia include systemic lupus erythematosus, lichen planus, persistent bacterial or fungal infections, and skin cancer. The skin may also be damaged from burns, other physical injuries, and radiation therapy.
Diagnosis
Doctors diagnose male-pattern or female-pattern hair loss based on its typical appearance. Determining the cause of other types of hair loss simply by observation is sometimes difficult. Doctors usually gently pull or pluck out a few hairs and examine the hair shafts under a microscope. Less often, doctors do a biopsy of the skin (see Diagnosis and Treatment of Skin Disorders: Diagnosis of Skin Disorders). A biopsy helps determine if the hair follicles are normal. If they are not normal, the biopsy may indicate possible causes. If the doctors' examination finds signs of hormonal irregularities or other serious illness, blood tests to identify those disorders may be needed.
Treatment
Male-pattern and female-pattern hair loss can sometimes be treated effectively with drugs.
Minoxidil may prevent further hair loss and increase hair growth when applied directly to the scalp twice a day. Finasteride works by blocking the effects of male hormones on the hair follicles and is taken by mouth daily. Improvement may occur after either of these drugs is 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. Finasteride is not used for women who have hair loss.
Hair transplantation is a more permanent solution, 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.
Telogen effluvium or anagen effluvium generally resolves after the inciting event or exposure to chemicals ends. 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. Another treatment for alopecia areata involves applying irritating chemicals, such as anthralin or other substances 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 will not grow back.
Last full review/revision August 2008 by Wendy S. Levinbook, MD
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