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Bleach does not technically colour the hair but removes existing colour to create a lighter result (see image The Influence of Bleach on Pheomelanin). Bleaches are usually combined with an oxidising agent, such as hydrogen peroxide, and an additional catalyst, for example ammonium hydroxide.
Bleaching involves two different steps. First, there is a dispersion and dissolution of melanin granules. This dissolution is associated with a change in colour from black to brown. This reaction is responsible for the resulting reddening that is often seen during the bleaching of dark hair. Following this dissolution phase, there is a much slower de-colouring phase. The exact biochemistry underlying these processes is not completely understood, but it is thought that the dissolution phase involves the destruction of different bonds maintaining the pigment particles while the de-colouring phase involves the breakdown of the polymeric structure of melanin. Following bleaching (bibliography 1), hair will often be different in texture and a conditioner will often be used either within the bleaching solution or after bleaching (bibliography 1). The use of products for coloured hair will maintain the condition.
Are colour products used with a high level of peroxide, for extra lifting capacity. High Lifting colours usually contain direct and pre-colour dyes (mostly for colour direction and not for adding colour depth) in favour of maximum lifting power.
Are usually colour products used with a very low level of peroxide, combining direct and pre-colour dyes to tone previously bleached or highlighted hair. Toners usually contain direct and pre-colour dyes; mostly for colour direction and not for adding colour depth.
1. Brown KC. Hair coloring. In: Johnson DH, editor. Hair and Hair Care. New York: Marcel Dekker.1997; 191-215.
