Hair thinning and hair loss

Hair, youíve either got too much or too little of it.

Many people consult their doctor concerned that they are losing hair. In the vast majority of cases there is nothing wrong and an understanding of the cycle of hair growth and reassurance is all that is needed.

This is the growth phase and this lasts for weeks or years. During this phase the hair grows about 1 cm every 28 days. Scalp hair stays in this active phase of growth for 2-6 years. The length of time that any individualís hair stays in the anagen phase is genetically determined. In late anagen, there is a gradual thinning of the hair shaft and a lightening of the pigment in the hair. This hair is then shed.
A signal (but it isnít known what or how) causes the hair follicle to enter the catagen phase.

This is a transitional phase that marks the end of anagen and can last for about 2 weeks. A club hair is formed when part of the hair follicle which is in contact with the lower portion of the hair, becomes attached to the shaft, cutting off the blood supply and effectively causing the shedding of the hair.

This is a resting phase that lasts for a few weeks. During this time, the hair follicle is completely at rest and the club hair is completely formed. At any one time an average of 13% of follicle will be in the telogen phase and 1% in catagen. Assuming an average scalp has around 100,000 follicles, roughly 70 hairs are shed every day.

Telogen effluvium
This is when something causes an interruption of the normal cycle which results in an unusual progression of many hair follicles into the catagen and then telogen phase. This means that many more hairs are suddenly lost causing a diffuse thinning of the hair rather than any bald patches. There is nearly always a cause, such as an acute illness 3-6 months before the hair loss. Pregnancy is another well known cause of telogen effluvium. The hormonal changes of pregnancy produce a prolonged anagen phase; when the pregnancy is over, many hairs suddenly progress into catagen and then telogen with the result that suddenly the woman seems to be losing their hair. In fact the hair is simply returning to its pre-pregnancy state.

Other causes of telogen effluvium are

  • Drugs
  • Thyroid disease
  • Crash dieting
  • Surgery
  • Low iron stores
  • Alopecia areata causes hair loss in patches and rarely complete baldness. Read our article for further advice.

Further information

This article published on
28 November 2005

Next review date 11/1/2013


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