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Hair Loss

What Causes Hair Loss?

Last updated on:
29/03/2012

Contributing Author: Guy Slowik FRCS

The causes of hair loss vary, depending on the type:

Generalized Hair Loss

Abnormal hair loss may occur:

  • Following certain illnesses and infections
  • After prolonged vitamin deficiencies, or a deficiency of protein or iron
  • Because of a disorder of the thyroid gland, in which there is too little thyroid hormone circulating throughout the body, causing inadequate stimulation of activity in body cells
  • As a side effect of medication or medical treatment (for example, chemotherapy or radiation therapy for cancer)
  • Following exposure to some toxic substances such as thallium (thallium sulfate is widely used as a rat poison)

In these cases, the hair loss is not immediately obvious. Although growth stops at once in the hair follicles, the dead hairs are not shed from the scalp until about three months later, when they fall out from their roots.

Major illness, injury, high fever, major surgery, severe bleeding, and possibly even severe emotional stress may cause sufficient physical upset to shock the actively growing hair roots into the resting phase, possibly to conserve energy that will be needed by the body for physical repair.

The roots remain securely anchored for three months, so there is no immediate apparent effect on hair growth following the illness or injury. But three months later, the hair sheds, and this may continue for some weeks.

Since this process does not damage the hair roots, they start to regrow - but it might be several weeks or months before new hair becomes apparent. Scalp hair grows at a rate of about 1 centimeter (around half an inch) per month.

Need To Know:

Cancer Treatments and Hair Loss

Anticancer treatments are designed to destroy rapidly growing cells, whether by chemotherapy drugs or with radiation. The hair root consists of extremely active cells, which during the active growth phase are growing and multiplying briskly to produce new hair cells.

Hair cells are very susceptible to anticancer treatments, targeted as these are against the most actively growing cells in the body. Fortunately, there is rarely any permanent damage. Hair growth usually returns to normal after therapy is completed.

Patchy Hair Loss

Patchy hair loss can be caused by:

  • Ringworm. Small patches of hair loss associated with dandruff-like scaling of the scalp and stubby, broken hair shafts within the bald area is typical of scalp ringworm. It occurs in children and is highly contagious, but it is not a serious threat to health. Once the diagnosis is made, the condition is easily treated with anti-ringworm treatment.
  • Alopecia areata. This condition involves patchy hair loss with normal underlying skin; the cause is unknown. As the hair in one patch starts to grow again, another bald patch may develop elsewhere. No cure for this condition is known, but it usually clears up by itself in six months to a year.

Need To Know:

In alopecia areata, it is rare for all scalp hair to be permanently lost. But this is more likely:

  • If the alopecia begins early in life,
  • If it persists over a long period, or
  • If it covers the scalp extensively.

Balding In Men

Balding is a normal process that develops to some degree in all men. It is influenced by male sex hormones, called androgens. Hormones are chemical messengers produced by the body that stimulates activity by organs or tissues elsewhere in the body.

There also is a strong inherited factor in balding. The trait can be inherited from either the mother's or the father's side of the family. It can affect both men and women, although women with this inherited tendency do not become completely bald.

The process of balding is due to progressive miniaturization of individual hair follicles, which become smaller and have a shorter growth cycle. The hairs consequently become smaller and narrower. The number of hair follicles remains the same, however. There is the same number of hair follicles in the scalp of a bald man as in the scalp of a man with a full head of hair.

The very first signs of the effects of androgens on scalp hair growth occur soon after puberty, which is the stage in the human life when the reproductive organs reach maturity. In boys, puberty occurs around age 13. After puberty, the front hairline above the temples may recede. In some men, this may be as far as the balding process will develop.

There is tremendous variation in the extent to which individuals may lose hair.

  • Some men experience a recession of the front hairline above the temples while retaining hair in the middle, which creates an "M" shape in the hairline above the temples and forehead.
  • Some lose hair on the center of the scalp, which produces a "bald spot" surrounded by hair.
  • Others have the recession at the front of their scalp join up with this area to create a larger balding area.
  • Some develop uniform thinning of the hair over the top of the scalp, with no discernible pattern; this usually progresses to complete baldness.

Nice To Know:

In men who will become completely bald, the majority will lose their hair at a young age and will complete the balding process by their mid-thirties.

 

 
 

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From Andrew Maynard - Chair of the University of Michigan Department of Environmental Health Sciences, with help from David Faulkner - 2013 Master of Public Health graduate.