The portion of hair that is seen is called the hair shaft. That which is below the surface of skin is the follicle. During our lifetime, each hair follicle undergoes repeated cycles of growth, rest, and regeneration. Hair loss can occur due to disturbances of the hair cycle, damage to the hair shaft, or disorders affecting the follicle.
DISTURBANCES OF THE HAIR CYCLE
Normally the majority of scalp hair is in the growth phase. A small percentage of hairs in the resting phase are shed each day (100-200 hairs shed daily). Under certain circumstances a higher percentage of hairs enter the resting phase and a woman may notice a sudden increase in hair shedding. Common causes include high fever, childbirth, severe infections, severe “flu,” severe chronic illness, major surgery, thyroid disorder, crash diets, inadequate protein intake, and certain drugs. The shedding often starts months after the inciting cause but will stop after several weeks if the offending cause is removed or corrected.
DAMAGE TO THE HAIR SHAFT
Hair is composed primarily of the protein keratin, which is the same substance that forms fingernails and toenails. Sulfur crosslinks between hair proteins provide for the strength of the hair. Damage to the hair shaft by improper cosmetic techniques can cause hair breakage. There is little damage from normal dyeing, bleaching, waving, or straightening. However, breakage can occur from too much tension during waving, from waving solutions left on too long or improperly neutralized, from waving and bleaching on the same day, or from too frequent hair treatments. Other causes of hair breakage include excess tension in braids, ponytails, and cornrows, or excess friction due to helmets or orthodontic appliances. Hair breakage will stop if the cosmetic procedure is stopped and the hair is handled gently, but hairs already broken cannot be mended.
DISORDERS AFFECTING THE FOLLICLE
Hereditary hair thinning, or androgenetic alopecia, is the most common form of hair loss in humans. This condition is also known as male-pattern hair loss or common baldness in men and as female-pattern hair thinning in women. Onset may occur in either sex at any time after puberty. It is estimated that half of the population experiences hereditary hair loss by age 50.
The cause of hereditary hair thinning is a gradual shrinkage of the hair follicle, which occurs under the influence of androgens. The smaller hair follicle results in a finer and shorter hair shaft. Women with hereditary thinning usually first notice a gradual thinning of their hair, mostly on the top of their heads, and their scalp becomes more visible. Over time, the hair on the sides may also become thinner. The patient may notice that her “ponytail” is much smaller. This diffuse thinning of the hair can vary in extent but it is extremely rare for a woman to become bald. Extensive laboratory tests are usually not needed if the woman with hereditary thinning has normal periods, pregnancies, and hormone levels. Thyroid disease and iron deficiency are two causes of hair thinning that can easily be ruled out by laboratory tests. Treatment for women with hereditary thinning includes topical minoxidil solution that, when used regularly, can partially reenlarge the miniaturized hairs.
Alopecia areata is an autoimmune disease that affects almost 2% of the population in the United States. Inflammatory cells target the hair follicle, thus preventing hair growth. Typically a small round bald patch is noticed; this patchy hair loss may regrow spontaneously. In other cases there can be extensive patchy hair loss and in rare cases there is loss of all scalp and body hair (alopecia areata universalis). Alopecia areata occurs equally in males and females, at all ages, although young persons are affected most often. Alopecia areata typically has a relapsing and remitting course. Treatment is available when the disease is active but does not prevent future occurrences of hair loss.
SEE ALSO: Autoimmune disorders, Skin care, Skin disorders
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- Olsen, E. A., Hordinsky, M., Roberts, J. L., & Whiting, D. A. (2002). Female pattern hair loss. Journal of the American Academy of Dermatology, 47(5), 795.
- Price, V. H. (1999). Treatment of hair loss. New England Journal of Medicine, 341, 964-973.