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Hair Loss

What Is Hair Loss?

The loss of hair (alopecia) is a natural phenomenon in all hair-baring animals that normally occurs during the hair growth cycle. It is estimated that most individuals (assuming they have a full head of hair) lose about 100 scalp hairs over a 24-hour period. Hair loss can become a cosmetic problem when it occurs in the wrong place at the wrong time in the wrong individual. True hair loss should be distinguished from damage to the hair shaft, which may cause breakage close to the scalp. This sort of damage is often caused by exogenous chemicals used to alter the physical characteristics of the hair shaft (hair dye, etc.) or other forms of self-manipulation.

Physicians divide cosmetically significant hair loss into two categories.

  1. Scarring alopecia: This sort of irreversible hair loss is characterized by damage to the underlying skin which results in scarring that destroys the hair follicle and its potential for regeneration. A simple visual examination is usually sufficient to diagnose this problem, although occasionally a biopsy may be necessary. Certain skin diseases as well as physical trauma produce this sort of damage.
  2. Non-scarring alopecia: This potentially reversible type of hair loss is very common and can be due to many causes, including certain diseases, drugs, aging, diet, as well as a genetic predisposition for hair loss called androgenetic alopecia (common balding).

There are three cycles of hair growth: growing (80% of follicles), resting, and shedding. In human hair, each follicle cycles at its own individual rate as opposed to most animals, where these cycles change with the season, and all hairs are in the same part of the cycle at the same time. This is why animals grow a thicker coat in the fall and shed most in the spring and why human beings do not shed. Unlike most animals, in humans, each hair has its own pattern of growing, resting, and shedding.

  • Each person sheds hair and regrows hair every day.
  • When this balance is disturbed and more hairs are shed than are regrown, alopecia or hair loss results.
Medically Reviewed by a Doctor on 11/21/2017

Patient Comments & Reviews

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Hair Loss - Causes

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Hair Loss - Home Remedies

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Women's Hair Loss

Hair loss doesn't only happen to men. There are a variety of causes of hair loss in women, including hormone problems, childbirth, PCOS, alopecia areata, and ringworm, among others.

See pictures of other causes of women's hair loss, and learn about treatments for thinning hair.


Read What Your Physician is Reading on Medscape

Alopecia Areata »

Alopecia areata is a recurrent nonscarring type of hair loss that can affect any hair-bearing area.

Read More on Medscape Reference »


Medical Dictionary