Hair dyeing

Additionally, hair may vary substantially in both chemical and physical composition, depending on race, hair colour, environment and a variety of other factors. Conditions of application are quite restrictive allowing very limited ranges of pH and temperature and, to a lesser extent, time. Only physiologically acceptable environments are used and limited adsorption and/or diffusion at room temperature precludes the use of many traditional dyestuffs.

The dyeing of hair may be more accurately described as staining, since significant amounts of dyestuffs are washed away and not utilised. Finally, the exposure of the user to both dye precursors and finished dyestuffs demands rigorous toxicological testing and acceptable profiles for all materials.