The dyeing of keratin fibres, and in particular human hair, with dye compositions containing oxidation dye precursors, generally called oxidation bases, such as ortho- or para-phenylenediamines, ortho- or para-aminophenols and heterocyclic compounds, is known. These oxidation bases are colourless or weakly coloured compounds which, when combined with oxidizing products, can give rise, by a process of oxidative condensation, to coloured compounds.
It is also known that it is possible to vary the shades obtained with these oxidation bases by combining them with couplers or dyeing modifiers, the latter being chosen in particular from aromatic meta-diaminobenzenes, meta-aminophenols, meta-diphenols and certain heterocyclic compounds, such as indole compounds and pyridine compounds.
The variety of molecules used in terms of oxidation bases and couplers makes it possible to obtain a rich palette of colours.
The “permanent” dyeing obtained using these oxidation dyes must, moreover, satisfy a certain number of requirements. Thus, it must not present any problem of a toxicological nature, it must make it possible to obtain shades of the desired intensity and must have good resistance to external agents such as light, bad weather, washing, permanent waving, perspiration and rubbing.
The dyes must also provide coverage of white hair, and finally must display minimum selectivity, i.e. ensure that the smallest possible differences in coloration are obtained all the way along the same keratin fibre, which generally is differently sensitized (i.e. damaged) between its tip and its root.