Structure of Hair & Hair Growth Cycle

Structure of Hair

Hair is made from strong structural protein known as keratin. This is of exactly the same protein from which the nails and outer skin layer is comprised.

A strand of hair comprises three layers:

  1. The innermost layer (known as the medulla) – only present in large thick hairs;
  2. The middle layer (known as the cortex) – which gives the hair its strength, texture and colour;
  3. The outermost layer (known as the cuticle) – a thin and colourless layer that protects the cortex.

Hair root structure

The hair’s root, enclosed within a follicle, lies below the surface of the skin. At the follicle’s base is found the dermal papilla, which is fed by the bloodstream. The blood carries the nourishment required to produce new hair. Containing receptors for male hormones and androgens, the dermal papilla is crucial to the process of hair growth.

It is the androgens that determine hair growth, and in the scalp hair of individuals who are genetically predisposed to hair loss in this area, they can cause the hair follicles to become progressively smaller and the hairs finer.

Hair structure diagramme

The Growth Cycle of Hair

Hair follicles grow in repeating cycles. A cycle comprises three distinct phases:

  1. Anagen – the phase of active growth
  2. Catagen – a transitionary phase
  3. Telogen – the phase of rest

Each hair passes through the three phases, totally independent of the current phase of its neighbouring hairs.

The hair growth cycles play an important role in the hair removal treatment. Excessive hair growth can be due to a number of reasons: heredity, stress, medication, and hormonal changes. In women, puberty, pregnancy and menopause play important parts in determining hair growth. Researchers say that there can be as many as 2500 hair follicles per square inch, although less than 100 hairs will be visible at any given time.

For these reasons, for purposes of treatment, it is very difficult to predict the exact length of time before there is no further hair growth in the treated area.

Anagen Phase – active growth phase

This is the ideal stage for treatment. The hair is grown, being visible above the skin, and can be treated. The hair shaft is attached to the papilla, thus enabling the laser to attack the melanin in the shaft and disable the papilla. For facial and body hair, this period can be as long as two to three weeks.

Catagen Phase – transitional phase

At the end of the Anagen phase the hairs enters into the Catagen phase. During this phase the hair follicle shrinks to about one-sixth of its usual length. The lower part is destroyed and the dermal papilla breaks away to remain below. At this stage the growth process is in reverse and the hair is preparing to shed. Note that this is not the same shedding process as post-laser treatment. However it is still possible to treat it with laser light since a follicle treated in the Catagen phase will still produce another hair. The duration of this stage is particularly variable and can be as short as two days.

Telogen Phase – resting phase

The Telogen Phase is the final stage. The hair is neither developing nor growing. Since it is not usually visible above the skin, the hair can not be treated during this phase. The hair shaft has detached fully from the papilla, in laser treatment not allowing the laser to attack the melanin in the shaft and disable the papilla. The length of this phase is unpredictable and can be as short as a few days or as long as a few years.

At the end of the Telogen phase the hair follicle re-enters the Anagen phase (Mesanagen). The dermal papilla and the base of the follicle join together once again, resulting in the commencement of the formation of a new hair. If the old hair has not already shed, the new hair pushes the old one out and the growth cycle recommeces.

To learn more about our anti-aging and rejuvenation treatments, to request a consultation or get advice, please contact us on +44 20 7580 8001 or through our online form.
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