Bleaching (bibliography 1) involves partial or complete de-colouring of the existing natural melanin content of the hair. The most commonly used method involves the use of an alkaline solution of hydrogen peroxide (H2O2). Hydrogen peroxide is usually stored in acid solution and is mixed just before use with an alkali-containing base. The alkaline solution is necessary since bleaching decreases with acidic pH; ammonia is most commonly used as an alkali as it appears to give the best bleaching results. Thickeners are usually added to give a thicker yet easy-to-spread consistency to the preparation. The degree of bleaching will vary with contact time; darker hair will need more time. Most often, a toner will be used to attenuate the result (bibliography 2).
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 2), hair will often be different in texture and a conditioner will often be used either within the bleaching solution or after bleaching (bibliography 2). The use of products for coloured hair will maintain the condition.
1. Bolduc C, MD, FRCPC, Shapiro J, MD, FRCPC. Hair Care Products: Waving, Straightening, Conditioning and Coloring. Clinics in Dermatology 2001; 19:431-436.
2. Brown KC. Hair coloring. In: Johnson DH, editor. Hair and Hair Care. New York: Marcel Dekker.1997; 191-215.
