Permanent hair colour works by interacting with the natural pigment of your hair and changing your hair’s structure. The dyes in permanent haircolor are actually tiny colourless molecules. With the help of ammonia, they penetrate the hair cuticle, but it’s not until they’ve combined with hydrogen peroxide and create a chemical reaction known as oxidation that the magic happens. Through oxidation, the permanent hair colour molecules turn complex and can embed themselves in the structure of the hair fiber. The result is what we know to be permanent hair colour, or at the very least, hair colour that can definitely withstand multiple washes.
One of the biggest reasons permanent hair colour gets a bad rap is because it consists of more potent chemicals than demi-permanent hair colour, which instead coats the hair, but doesn’t alter the structure of it. Permanent hair colour also opens up the cuticle and needs to sit on the hair longer, so hair texture might change slightly.