The bleach begins to work as soon as it comes into contact with the hair. The hair swells and the cuticle lifts, allowing the bleach to penetrate the cortex of the hair. Oxygen is released from the peroxide which reacts with the natural hair pigments known as Melanin, Pheomelanin and Trichosiderin , making them colourless.

Bleaching the hair changes the colour through the colour spectrum, for example dark brown hair through to warm red to a very pale yellow. The shades and the final colour depend on the original colour of the hair. 

www.birminghamtrichologycentre.co.uk