Chapter 4 125 Hydroxyl radicals can also be formed in the presence of redox active metals such as iron and copper, which are present at low levels in the melanin particles (Eq. 2). The hydroxyl radicals are also strong oxidants which will decolorize melanin. Fe2+ + H2O2 Fe3+ + HO* + HO- Eq. 2 The products produced from the bleaching of melanin have not been characterized and it is likely that a wide range of species are formed. A possible route to breakdown of the chromophore is shown in (Eq. 3). The products of the breakdown are likely polycarboxylates and polyols with a range of molecular weights. OH OH N H O O N H COO - COO- N H Eq. 3 Ammonia is important in the lightening process not just as an alkalizer to increase the pH to form the perhydroxyl anion, but it also disintegrates the melanin particle itself to aid penetration of the oxidizing species into the melanosome granule. The ammonia does this by disrupting the lipid membrane that surrounds the granule giving access to the colored bleachable species.8 The amount of lightening achieved can be altered by changing the concentrations of hydrogen peroxide and ammonia. The concentration range of hydrogen peroxide used is typically 3% to 8% depending on the shade. The extra high lift blondes are at 6% or 8%, the light blondes at 4.5% and the medium blondes and darker shades at 3%. Higher levels of hydrogen peroxide are not used due to regulatory restrictions. Free ammonia levels range from 0.7% to 2.0%. The amount of lift will be assessed by the hair stylist in terms of levels of lightening or lift, and can, if desired, be measured using a spectrophotometer in terms of the change in the L value in the L,a,b