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What Is Hair Loss?
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Hair grows everywhere on the human skin except on the palms of our hands and the soles of
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our feet, but many hairs are so fine they're virtually invisible. Hair is made up of a protein
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called keratin that is produced in hair follicles in the outer layer of skin. As follicles produce
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new hair cells, old cells are being pushed out through the surface of the skin at the rate of
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about six inches a year. The hair you can see is actually a string of dead keratin cells. The
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average adult head has about 100,000 to 150,000 hairs and loses up to 100 of them a day;
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finding a few stray hairs on your hairbrush is not necessarily cause for alarm.
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At any one time, about 90% of the hair on a person's scalp is growing. Each follicle has its
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own life cycle that can be influenced by age, disease, and a wide variety of other factors.
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This life cycle is divided into three phases:
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• Anagen -- active hair growth that lasts between two to six years
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• Catagen -- transitional hair growth that lasts two to three weeks
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• Telogen -- resting phase that lasts about two to three months; at the end of the resting
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phase the hair is shed and a new hair replaces it and the growing cycle starts again.
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As people age, their rate of hair growth slows.
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There are many types of hair loss, also called alopecia:
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• Involutional alopecia is a natural condition in which the hair gradually thins with age. More hair
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follicles go into the resting phase, and the remaining hairs become shorter and fewer in number.
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• Androgenic alopecia is a genetic condition that can affect both men and women. Men with this
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condition, called male pattern baldness, can begin suffering hair loss as early as their teens or
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early 20s. It's characterized by a receding hairline and gradual disappearance of hair from the
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crown and frontal scalp. Women with this condition, called female pattern baldness, don't
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experience noticeable thinning until their 40s or later. Women experience a general thinning
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over the entire scalp, with the most extensive hair loss at the crown.
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• Alopecia areata often starts suddenly and causes patchy hair loss in children and young adults.
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This condition may result in complete baldness (alopecia totalis). But in about 90% of people
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with the condition, the hair returns within a few years.
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• Alopecia universalis causes all body hair to fall out, including the eyebrows, eyelashes, and
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pubic hair.
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• Trichotillomania, seen most frequently in children, is a psychological disorder in which a person
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pulls out one's own hair.
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• Telogen effluvium is temporary hair thinning over the scalp that occurs because of changes in
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the growth cycle of hair. A large number of hairs enter the resting phase at the same time,
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causing hair shedding and subsequent thinning.
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