Hair Coloring 144 slowly build-up the desired color. Shades can thus be unpredictable and use is limited to men’s products as a color restorer to gradually cover gray. Bleach Products The hydrogen peroxide oxidant used in Permanent Level 3 products is not always sufficient for the level of lightening required by a given consumer. For example, to change from a dark brown to a light blonde with a coloring product will not be possible and in these cases a bleach product is used. Bleach products are also often used for highlighting where high contrast is required between the lightened hair and the original hair color. Essential components of a bleach product are hydrogen peroxide and a persulfate salt, typically a mixture of potassium persulfate and ammonium persulfate. Also required is an alkalizer to give a final buffered pH of ~ 10. Persulfate salts are typically sold as a powder, and a powdered silicate such as sodium silicate is added to increase the alkalinity. The powder is then mixed directly with the hydrogen peroxide liquid formula to form a thick paste or with the hydrogen peroxide formula and an ammonia-containing formula to form a thinner cream or gel that can be more easily applied to the whole head. Persulfate salts act as a booster for the lightening performance of the hydrogen peroxide, enabling much more dramatic changes in hair color. The exact chemistry is not known, but it is hypothesized that the perhydroxyl anion formed at alkaline pHs from hydrogen peroxide (as previously shown in Eq. 1) reacts with the persulfate to form a more reactive sulfate radical anion. This radical can react further with hydroxyl ions and water to form highly reactive hydroxyl radicals. (See Eqs. 8 through 10 below.) It is likely a combination of all these reactive species that are activating the bleaching of melanin and the lightening of hair.