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Hair Loss

What Is Hair Loss?

Last modified: 
16/04/2013 - 12:58

Contributing Author: Guy Slowik FRCS

Most people routinely lose between 70 and 150 hairs from their scalp each day, mainly through washing, brushing, and combing.

Scalp hair starts to thin when more hairs are lost through normal shedding than the scalp is able to renew. About 40% of the density of scalp hair has to be lost before thinning of the hair becomes noticeable.

Hair loss can be caused by:

  • Heredity. Most balding is caused by a genetic predisposition - in other words, it's part of a person's genetic makeup. This is called male pattern baldness, or hereditary balding or thinning. It is the most common cause of thinning hair.
  • Illness, certain physical conditions, or their treatments. This can include high fever, thyroid disease, childbirth, inadequate protein in the diet, iron deficiency, cancer treatments, the use of certain medications, and other causes.

Hair may be lost in two ways:

  • In patchy hair loss, well-defined areas of hair are lost while the remaining scalp retains a good covering of hair.
  • In generalized hair loss, there is a uniform thinning over the entire scalp with no areas of normal hair growth.

The medical term for hair loss is alopecia. There are different classifications of alopecia:

  • Alopecia areata is a disease in which well-defined bald patches occur. It usually clears completely within 6 to 12 months without treatment.
  • Alopecia totalis is an uncommon condition in which all hair on the scalp is lost. The cause is unknown, and the baldness is usually permanent.
  • Alopecia universalis is a total loss of hair on all parts of the body.
  • Androgenetic alopecia is balding caused by heredity. It can affect both men and women, although women with this inherited tendency do not become totally bald. The condition can start in a person's teens, twenties, or thirties.

Nice To Know:

The story of Samson and Delilah illustrates how, in the popular imagination, strength and virility have long been associated with an exuberant growth of hair - Samson's source of strength was his hair, which Delilah had shaved in betrayal of him. Indeed, many societies have shaved the scalp as a form of punishment.

Today, however, more men are feeling comfortable with baldness. More celebrities and athletes are sporting bald heads, helping to dispel the myth that youth or masculinity are linked to a full head of hair.

The Structure Of Hair

Every hair grows within a hair follicle, which is a tiny tube of cells close to the surface of the skin. Each hair has a root and a shaft within this follicle.

If you pluck a hair and hold it up to the light, the root will appear as a bulbous white swelling at the deep end. The root lies between 2 and 4 millimeters (about a tenth of an inch) under the skin surface. Its purpose is to produce the actual hair, which is known technically as the hair shaft.

The hair shaft contains no living tissue. It consists of protein material twisted into a very fine rope-like arrangement. It is this part of the structure that we think of in everyday terms as "hair."

Each hair has:

  • sebaceous gland, which provides fats and greases to the hair
  • An erector muscle, which is responsible for lifting the hair off the surface of the skin at times of stress or to conserve warmth

The hair root does not grow continuously, but rather in a cycle of stops and starts.

  • There is an initial period of active growth that lasts about three years.
  • As the period of growth ends, the deepest part of the hair follicle wastes away.
  • The hair root then enters a resting period of about 90 days, during which no further hair is produced by the resting root.
  • At the end of this phase, the hair falls out and a new hair is produced.

Human hairs are randomly distributed all over the scalp in terms of their growth pattern, so that at any one time, some hairs will be actively growing while others are resting. Only those hairs ending their resting phase are lost each day.

There is tremendous variation in the number of hairs that people shed each day, depending on the number of scalp hairs and the length of the growth cycle. As people age, their rate of new hair growth slows down, resulting in a gradual thinning.

Need To Know:

Q: What should I do if I think I'm losing more hair than normal?

A: If you notice you are shedding hair excessively after combing or brushing, or if your hair is becoming thinner, you should consult with your primary care provider or a dermatologist (a physician who specializes in treating skin and hair problems). A doctor can determine if disease is present and whether or not the hair loss will respond to medical treatment.

Facts About Hair And Hair Loss

  • The average human scalp has about 100,000 hairs.
  • Nearly two out of every three men develop some form of balding, while a higher percentage of men and women have some form of hair loss during their lives.
  • About 90% of a person's scalp hair is in a continual growth phase that lasts two to six years.
  • The other 10% of scalp hair is in a resting phase that lasts between two and three months.
  • Between 70 and 150 hairs are regularly lost from the scalp each day.
  • People with blond hair typically have more hair (average 140,000 hairs) than the average brunette (105,000 hairs) or redhead (90,000).
  • About 40% of the density of scalp hair has to be lost before thinning of the hair becomes noticeable.
  • Shaving hair does not stimulate hair growth.
  • Hair plucking does not stop hair growth.
  • Hair grows faster in warm weather than in cold.
  • Hair grows at an average rate of 1 centimenter (around half an inch) per month.

 

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Hair Loss

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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.