It is present practice to bleach human and other hair by the action of agents which evolve active (i.e., nascent) oxygen. These agents decolorize the pigment in the hair. The agents which are the most commonly used for the purpose are hydrogen peroxide, sodium perborate, sodium persulfate, percarbamide, and melamine perhydrate, and their decolorizing action is direct. It is also present practice to employ these oxidizing agents in the dyeing of hair with dyes which develop their coloration by oxidation, to provide the necessary oxidation component. The action of the oxidizing agent in the hair coloration here is indirect.
A disadvantage of the aforesaid bleaching and dyeing processes is that the oxidizing agents used therein damage the substance of the hair to greater or less extent and so degrade it.
The damage which these oxidizing agents cause the hair is manifested by impairment of various properties of the hair such as its breaking strength, "feel" (akin to scroop), gloss and flexibility, so that the hair may actually become brittle. The agents increase the alkali solubility of the hair and this is the damage which is the most easily measurable. The damage is caused by the active (nascent) oxygen which these compounds evolve during their use on hair.
In the past, efforts have been made to find compounds which would mitigate or decrease the disadvantageous effects of the aforesaid oxidizing agents. Thus it has been proposed to add to hair bleaching and dyeing solutions certain 1-hydroxyalkane-1,1-diphosphonic acids and 1-aminoalkane-1,1-diphosphonic acids such as 1-hydroxyethane-1,1-diphosphonic acid, 1-aminoethane-1,1-diphosphonic acid, 1-aminobenzyl-1,1-diphosphonic acid or 1-hydroxyhexane-1,1-diphosphonic acid. Furthermore, aminopolyphosphonic acids having at least three phosphonic acid radicals in the molecule have been proposed for the purpose, such as aminotri-(1-ethyl-phosphonic acid), ethylenediaminetetra-(1-ethylphosphonic acid), aminotri-(1-propylphosphonic acid) and aminotri-(isopropylphosphonic acid). Even though these compounds have provided a considerable decrease in the damage to hair, a demand exists for compounds which will further reduce the damage to the hair in view of the increasing and more frequent use of oxidizing agents in bleaching and dyeing processes by hairdressers.