Permanent Hair Color

All "permanent" haircolor products and lighteners contain both a developer, or oxidising agent, and an alkalizing ingredient as part of their ammonia or an ammonia substitute. The purpose of this is to:

• raise the cuticle of the hair fibre so the tint can penetrate,
• facilitate the formation of tints within the hair fibre,
• bring about the lightening action of peroxide.

Permanent hair-coloring products consist of two components that are packaged separately and mixed together immediately before application. One package contains a solution of hydrogen peroxide (usually 6%) in water or a lotion base. The other package usually contains an ammonia solution of dye intermediates and preformed dyes—called couplers. The primary intermediates are ortho or para diaminobenzenes, aminohydroxybenzenes, and to a lesser extent dihydroxybenzenes that develop color on oxidation. The color couplers don't oxidize readily but react with the oxidized primary intermediates to provide a wider variety of colors. The couplers are phenols, meta disubstituted phenylenediamines and phenyleneaminophenols, and various resorcinol (1,3-dihydroxybenzene) derivatives.

As soon as the ammonia dye solution and the hydrogen peroxide solution are mixed together, they are applied to the hair. The ammonia in the mixture (less than 1% concentration) causes the hair to swell and the cuticle scales to separate a little. After this happens, the dye precursors are able to penetrate the cuticle before they have fully reacted with each other and with the hydrogen peroxide. This is why even when brown hair coloring is first applied it looks whitish. This is also why you have to wait a half hour or more for the color to develop.

Darker shades are obtained by using higher concentrations of intermediates. Tones can also be adjusted. For example, addition of resorcinol will make a shade more yellow, while adding 4-amino-2-hydroxytoluene will make the shade redder. Sometimes dyes are used along with the oxidation dye intermediates to add vibrancy to the tone that is not otherwise available. Usually these dyes are used to add intensity to gold or red shades.