Chapter 1 – Back to the Basics

1.2 Trichology – The Science of Hair

When you are colouring hair, why must you consider the hair itself?

The Hair Strand

Each hair strand is made up of 3 layers:

  • Cuticle – the outer covering made up of overlapping layers of scales. How these scales sit directly affects it’s porosity, which determines how the hair will absorb moisture and chemicals.
  • Cortex – the second layer, gives hair its strength and elasticity and also houses melanin, which is the basis of natural hair colour.
  • Medulla – The inner core, or pith, of the hair strand gives hair its structure and is often missing from very fine hair.

A diagram of a magnified hair strand, depicting the location of the cuticle, cortex, and medulla.

These various structural properties of the hair itself, as well as the hair’s natural melanin, will have a direct influence on the end result of a colouring service.


Firstly, let’s revisit melanin. What is it, and why is it important?

There are two types of melanin that reside within the cortex of the hair strand:

  • Eumelanin – black or brown pigment
  • Pheomelanin – red or yellow pigment

Varying combination, concentration, and size of these two pigments produce every natural hair colour that exists. For example:

A heavy concentration of eumelanin, with a sprinkling of pheomelanin, results in dark brown or black hair:

An enlarged cross section of dark brown hair showing much more eumelanin than pheomelanin.

A light concentration of eumelanin, with a sprinkling of pheomelanin, results in light brown or blonde hair.

An enlarged cross section of blonde hair showing only a bit of eumelanin and much less pheomelanin.

A heavy concentration of pheomelanin, with a good amount eumelanin, results in a deep Auburn red shade of hair.

An enlarged cross section of auburn hair showing around equal amounts of eumelanin and pheomelanin.

When hair is lifted with an oxidative colour or bleach, eumelanin is more easily obliterated than pheomelanin. This becomes more apparent when you look at the underlying pigments at each of the ten levels:

The 10 levels of hair colour and their corresponding underlying pigments, ranging from black to palest yellow.

Notice how the underlying pigments range from dark red to palest yellow. This is because pheomelanin is tougher to remove, so when a client tells you that their hair “lifts warm,” you can assure them that that is the case for everyone!

When hair is coloured, the underlying pigment will affect the formula based on whether you want to neutralize or enhance these warm pigments. For example, does the client desire a cool chocolate brown hair colour or a more golden-brown hue? You will then use the colour wheel to create an appropriate formula.

When going darker with a low-level developer, the underlying pigment will not be exposed, but you still must consider the existing tone of the client’s hair when formulating for the desired result.

Hair Condition

When consulting with a client, you must also assess the condition of the hair. There are three main characteristics to look at: Porosity, elasticity, and texture. All three physical factors will influence which products to choose and how to process the colour.


Porosity refers to the hair’s ability to absorb moisture or chemicals. Porosity is influenced by how the cuticle scales sit in relation to each other.

An enlarged diagram showing the porosity of three different strands of hair. Described in following text.Resistant Porosity            Average Porosity           Extreme Porosity


Elasticity is the hair’s ability to stretch and return to its original shape without snapping.


Texture refers to the diameter of the hair strand and is generally described as fine, medium, and coarse.

Cross sections of fine, medium and coarse hair strands.

Fine                          Medium                                     Coarse         

With these basics fresh in your mind, let’s move on to how the various colouring products work, and how to decide which product is best for the client.

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Hair Colour for Hairstylists: Level 2 Copyright © 2021 by Arden Magtiza is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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