Chapter 4 147 The two key reactive species (Eqs. 11 and 12) formed during the coloring process responsible for lightening of the melanin and color formation are also responsible for the hair structure changes. (1) The perhydroxyl anion (HOO-) formed from the hydrogen peroxide and high pH Eq. 11 (2) HO radicals formed from the reaction between hydrogen peroxide and redox metals such as copper and iron Eq. 12 Table 5 Summary of Colorant Technologies Hair Dye Product Dye Technology Level of Lastingness Level of change to hair structure Temporary Direct dyeing with FD&C and D&C dyes, no oxidant Wash out (with one wash) None Semi- permanent Direct dyeing with HC and disperse dyes, no oxidant Wash out (with 6-8 washes) None Demi- permanent Oxidative dyeing, reduced hydrogen peroxide concentration (1-2%) Wash out (with up to 24 washes) Slight to no level of change Permanent Oxidative dyeing, hydrogen peroxide (3-8%) Permanent (grows out) Medium level of change Bleaching Oxidative bleaching, no dye deposition, hydrogen peroxide (3-8%), persulfate salts Permanent (grows out) High level of change with multiple uses These species react with the different hair fiber components, leading to changes in the hair structure. We can divide the hair into different structural segments, i.e. the very top hair surface