Hair Biology 101

Christopher Stephens Salon West Palm BeachWhat is hair made of?  How does hair grow?  Why does it fall out?  These are just some of the questions we’ll answer here in this blog.  If you’re experiencing hair problems, our aim is to clarify why these problems occur and to help you find a remedy to your specific problem. But remember, excessive hair loss could indicate a medical condition, so you should first consult with your physician before trying alternative methods. Below, the make-up of hair will be broken down and explained along with possible reasons for hair loss.


Hair can be broken down into two parts: the hair follicle and the hair shaft.


The hair follicle is a tiny stocking-shaped structure buried deep in the scalp.  It is nourished by a vast supply of blood vessels and this is where hair growth takes place.  At the base of the follicle is the hair bulb.  It is an active structure that produces hair cells.  These cells multiply and divide to eventually form a long structure known as the hair shaft. 



Your smooth, glossy hairs are highly complex in structure.  Each hair can be compared to a tree: the moisture is found in its centre behind a tough, outer layer of protective ‘bark’.  If the ‘bark’ is stripped off to expose the centre, the hair may break.

This outer layer is called the cuticle.  It is made up of overlapping layers of long cells.  A healthy cuticle is more than just a protective layer - much of the shine that makes healthy hair so attractive is due to the cuticle.  Smooth cuticle cells reflect light from their surfaces.  This, together with the pigment in the cortex (see below), gives hair its characteristic appearance.

The centre part of the hair is called the cortex which makes up most of the hair shaft.  The cortex gives the hair its special qualities i.e. elasticity and curl.  It’s also packed with strands of keratin (a remarkably resistant protein).  These keratin fibres are compressed into bundles of larger fibres.  In turn, these large fibres are held together by a mass of sulphur-rich keratins.  This bundle is known as the matrix.  The matrix is extremely strong and can resist extensive stretching and twisting.

The cortex also contains granules of hair pigment known as melanin which is produced in the hair follicle.  There are two types of granules: smooth, dark granules and lighter granules.  These granules provide differing hair shades.

In some hairs, especially grey ones which actually contain no pigment, the cortex has a central core called the medulla. It is an air-filled structure more often present in thicker hairs.


From the moment hair starts to grow until the point at which it falls out, each hair passes through three growth stages:

  1. Anagen phase –known as the ‘active’ growth phase.  The hair shaft starts to grow inside the hair follicle.  This can last for 3–7 years.
  2. Catagen phase –known as the ‘intermediate’ phase and lasts between 2-4 weeks.  Pigment is no longer produced and the follicle stops producing hair.  The base of the follicle moves upwards towards the surface of the skin. 
  3. Telogen phase –the ‘shedding’ phase which can last for 3-4 months.  A new hair begins to grow from the hair follicle.  As it grows upwards, the old hair is naturally shed.  These hairs naturally fall out e.g. during shampooing or brushing.  Shedding is part of the normal regeneration process and a new hair emerges from the same place as the old hair.


Many experts believe there are a variety of factors that can cause hair to fall out.  These often include:

  • Hereditary factors
  • Natural ageing process
  • Poor nutrition
  • Nervous disorders
  • Hormonal imbalances
  • Serious illness
  • Chemotherapy or radiation treatment

If you or someone you know is experiencing abnormal hair loss, please consult with your physician.

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