What is Oxidation in Hair Colour?

Understand the science behind a key term often used when discussing hair colourants.

Oxidation takes place when an unstable atom loses an electron, thus allowing the atom to form a new compound with another element.

In the context of colouring hair, the oxidising agent hydrogen peroxide is used. When hydrogen peroxide is combined with a para-dye an ‘imin’ structure develops, creating a new compound called a meta-dye.

During the application stage, para-toluene-diamine (PTD), a small salt crystal is dissolved in the tinting cream. The alkali within the mix helps to soften the hair, opening up the cuticle layer and allowing the PTD dyestuff to enter the cortex.

Para-dyes are oxidised and polymerisation occurs, PTD para-dye crystals start to develop their colours and combine together at up to 300 times their normal size forming meta-dyes. Surplus oxygen reacts with existing natural hair pigments to produce a slight lifting effect.

When oxidation occurs, large flakes of pigment are created, which form the final permanent dyes within the cortex – the target shade is a specific mix of red, blue and yellow tones.