Hair and its stages of growth

Hair and its stages of growth

Hair and its stages of growth

Did you know? The average person sheds between 50 and 100 hairs a day. (2) The cycle of shedding and regrowth normally does not cause noticeable hair thinning on the scalp – as hair is shed, new hair is growing at the same time. Disruption of this cycle causes hair loss, as shed hair is not replaced as quickly or is virtually destroyed.

A hair follicle is essentially a pocket in the skin which anchors each hair that occurs on the body. The follicle, along with the shaft (the visible fibre on the surface of the skin) make up what we all know as hair. At the base of the hair shaft is the hair bulb, consisting of protein known as keratin. Tiny blood vessels in the papilla (cells surrounding the bulb) nourish hair follicles and also help to regulate hair growth and its structure by delivering hormones. Hair follicles are the structures which effectively function in cycles.

Three stages make up the lifecycle of hair follicles:

  • Anagen: The active growth phase
  • Catagen: A short transitional phase (between growth and shedding / resting)
  • Telogen: The resting and natural shedding phase

Illustration showing hair follicle cycle stages: anagen; catagen and telogen.

The cycle begins with growth and ends with shedding, before returning to a growth phase once more.
Depending on the location of the hair in the body, the length of anagen (growth) phase can vary greatly. Each human scalp hair follicle is known to produce hair for between 2 and 6 years (3) before resting for a few months. Hair in other parts of the body such as the eyebrows and lashes and on the limbs, has a significantly shorter growth phase lasting just 30 to 45 days, which is why the hair in these parts is generally shorter.

During the resting phase hair will be shed (fall out). It is estimated that there are approximately 100 000 hair follicles on a person’s scalp. Each hair follicle rests at a different time, and this means that while some are in the telogen (rest/shedding) phase, others are in the anagen (growth) phase at any given time. This is why sometimes hair loss or miniaturisation, wherein the hair follicle becomes narrower and finer, shorter, weaker hair is produced, can go unnoticed for a period of time.

When the normal hair cycle is disrupted, and the natural flow is no longer seamless, hair loss soon becomes more noticeable, especially if there is extensive damage to the hair follicle rendering it incapable of producing hair which is then replaced by scar tissue instead.

 References:

2. American Academy of Dermatology. Do you have hair loss or hair shedding?:https://www.aad.org/public/skin-hair-nails/hair-care/hair-loss-vs-hair-shedding [Accessed 20.11.2017]

3. ScienceDirect. January 1970. Journal of Investigative Dermatology. Human hair cycle:https://www.sciencedirect.com/science/article/pii/S0022202X15477954 [Accessed 20.11.2017]

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