The Anatomy of Hair

Hair Science 101:

Human hair is made up of two parts – the follicle in the skin and the shaft that we see.  It contains the sebaceous gland which produces sebum – the hair’s natural conditioner.

Human hair structure made of three parts:

  • Root – the widest part of the hair, growing in the hair follicle
  • Shaft – the middle length of the hair from root to tip
  • Tip – the end of the hair farthest from root where the hair is narrowest

Human hair (shaft) consists of three layers

  • The Medulla – the deepest layer of hair
  • The Cortex – the middle layer of the hair which provides the hair strength
  • The Cuticle – the keratin covered outer layer which protects the cortex

The Cuticle

The cuticle is covered with layers of overlapping cells which protect the hair’s inner layers.  This layer is colorless and permits light to shine through. Many of our styling products work to affect this layer.  Closed cuticles will hold moisture and in turn protect the cortex creating healthier hair.


The Cortex

The cortex provides the strength to the hair shaft and determines the color and texture of the hair.  It travels along the shaft from root to tip.  The cells of the cortex are bonded tightly together which allows for strength, elasticity and mass. This is the layer that is affected when changing the texture or color of the hair permanently.


Chemical Processes



Relaxers contain powerful straightening agents which affect the cortex of the hair.  To do this, they much open the cuticle completely to break down the bonds in the cortex and chemically straighten the hair.  Sodium Hydroxide, also an agent in drain cleaners, is used in relaxers with a PH of 10-14 – aka relaxers with “lye”.  Another straightening agent – guanidine hydroxide – is used in “no-lye” relaxers.

Permanent Hair Color

Again the cuticle layers must be lifted in order for this process to work and color to be deposited in the hair shaft.  Once the cuticle is opened the dye racts with the cortex to deposit or remove color.

If you process your hair make sure you understand what it is doing to your hair structure.  Understand how the styling products you use will benefit (or harm) your chemically altered hair.  It’s crucial to have a clear understanding of a products pH level and its effect on the cuticle layer of the hair.


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