Hair Coloring 122 2. An alkalizer: typically ammonia but ethanolamine is also used. The alkalizer plays a dual role in aiding the lightening of the melanin and formation of the dyes. It does this by buffering the reaction at a basic pH and aiding the penetration of the dye precursors into the hair. The final pH of the typical product is in the range of 9.8–10.3. 3. The dye precursors, which are oxidized by hydrogen peroxide to form the color inside the hair. The final color is a balance of the amount of lightening and the amount and type of dye precursors used. For example to create a blonde shade, the level of hydrogen peroxide is high (4.5%) and the level of dye precursors low ( 0.5%). For a black shade, a lower level of hydrogen peroxide (3.0%) is used with a much higher level of dye precursors ( 5%). Thus, controlling the components above will enable the two changes to occur simultaneously—the lightening of the underlying color and the deposition of color—to achieve the final desired color. Lightening: The ability to lighten the natural hair color is a crucial component of Level 3 permanent colorants. This is obvious if the consumer desires a lighter shade (e.g. the blondes) but it is also important for gray coverage and for vibrant shades. Most consumers wanting to cover gray also attempt to match their natural color, but just adding dyes will make the hair darker. To deliver the perfect gray coverage, both lightening the natural color and adding dyes are necessary. The same is true for vibrant shades such as reds and auburns. The color of the dyes is more obvious and vibrant if the underlying hair color is lighter. The natural color of hair is controlled by the type and amount of melanin and it is the melanin that is decolorized to lighten the hair. As aforementioned, there are two types of melanin: eumelanin, which is mainly found in brown hair and pheomelanin, found in red hair.3 Both melanins occur in the cortex of hair as insoluble particles called melanosomes which are ~ 0.5 µm in size. The melanosomes give the hair color both by light scattering and light absorption.4 Figure 1 shows a transverse section of dark hair using