How do Hair dyes really work?

Colouring your hair is the best way to change up your style, the colour you pick can reflect your character and personality. Recently, there has been a huge hype about crazy hair colors. I have seen the odd vibrant purple through to silver, but not many are aware of how this process works or what the cause of the damages are.

I am going to try and break it down for you in simple terms. Before we get into the chemistry of hair dyes, lets talk about the anatomy of hair.

cross section of hair

Hair consists of the cuticle, cortex and medulla:

  • Cuticle- the outer most layer, has many keratin cells overlapping each other, the layer is smooth but also very susceptible to mechanical and chemical damage
  • Cortex- forms bulk of the hair, contains natural pigments (melanin) the color our hair appears to be, and has a high moisture content
  • Medulla- usually only present in coarse hair, function is unclear

There are many chemicals in your hair dyes. The ones that we need to know about and are involved in changing your natural hair colour are hydrogen peroxide(blue), ammonia (green) and coloring precursors (purple).

hair dye ingredients

Now to the nitty gritty…

1- Ammonia is an alkaline agent and has the ability to lift the hair shafts on the cuticle, allowing the hydrogen peroxide to penetrate through.

2- Peroxide can then diffuses through the hair shaft into the cortex, where the melanin is found. The peroxide decolors the melanin, essentially removing your natural hair color.

3- The color molecules, also known as precursors, molecules small enough to penetrate into the hair shaft, can then replace your old color.

4- Once in the hair shaft the molecules join and enlarge, which prevents them to diffuse out of the cortex

5- An acidic agent usually citric acid (underlined in yellow above) e.g. conditioner is used to shrink, close and realign the hair shafts

Hair dye Science

This is a very simplified explanation of what happens, some detail may have been lost in translation but feel free to ask any questions, leave your comments and thoughts.

-xo S.


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