HOW HAIR COLOUR WORKS
Our hair primarily consists of a substance called keratin and is divided into three sections which are, from the outside in: the cuticle, cortex and medulla. Two proteins are found within the cortex and different ratios of these produce each person’s unique natural hair colour. When both are absent the result is grey hair.
Permanent hair dyes work by opening up the cuticle (usually with the aid of ammonia which has an alkaline pH), allowing the dye to enter and react in the cortex to deposit or remove colour. The developer, which contains hydrogen peroxide, bleaches the natural melanin pigment of the hair and acts as a catalyst for the oxidation process. The colour is infused into the cortex rather than painted over it. Finally, a conditioner (acidic pH) closes the cuticle to re-seal the hair shaft.