Oxidative Hair Coloration

Permanent Hair Colorants. Permanent colorants produce hair coloration that lasts until the hair grows out. Color is formed inside the hair by hydrogen peroxide-induced coupling reactions of colorless dye precursors. A hiU range of shades can be obtained with this system and the permanent or oxidative hair colorants are considered to be the most important class of hair dyes. 

Oxidation Hair Colorant. Color-forming reactions are accomplished by primary intermediates, secondary intermediates, and oxidants. Primary intermediates include the so-called para dyes, -phenylenediamine, -to1nenediamine, -aminodiphenylamine, and -aminophenol, which form a quinone monoimine or diimine upon oxidation. The secondary intermediates, also known as couplers or modifiers, couple with the quinone imines to produce dyes. Secondary intermediates include -diamines, w-aminophenols, polyhydroxyphenols, and naphthols. Some of the more important oxidation dye colors are given in Figure 1. An extensive listing is available (24,28). 

Bleaching of natural hair color can be done as a single cosmetic application but is also part of oxidative hair coloring. Bleaching, blonding, and lightening of human... 

Uses Emollient, skin conditioner in cosmetics surfactant, dye leveling agent, vise, control agent for oxidation hair color systems Trade Name Synonyms Lowenol S-216 [Lowenstein Dyes Cosmetics http //www.Jhlowenstein. com]... 

Krasteva M, Bons B, Ryan C, Gerberick F. Consumer allergy to oxidative hair coloring products epidemiologic data in the literature. Dermatitis. 2(X)8 20 123 1. 

Uses Surfactant, dye leveling agent, vise, control agent for oxidation hair color systems... 

Also present but not essential in permanent hair colorants are nitro dyes which dye hair without oxidation. These dyes, nitro derivatives of aminophenols and benzenediamines, impart yellow, orange, or red tones. Although they have good tinctorial value, they are not as colorfast as the oxidative dyes. They also are used in semipermanent hair colorants. 

Melanin Drying. One development (ca 1993) in hair coloring involves the formation of pigments within the hair that are very similar to natural melanin. Thus either catalytic or air oxidation of 5,6-dihydroxyindole [3131-52-0] can be effectively used to permanently dye hair within a short time (38). The formed color can, if required, be further modulated with dilute H2O2 or can be even totally removed from hair by this oxidant. 

The main dye prodncing system nsed in hair coloration involves the oxidation of a primary intermediate in the presence of a colonr coupler to produce the coloured molecule. The primary intermediates are 1,4-phenylenediamines or 1,4-aminophe-nols and the colonr conplers are 1,3-phenylenediamines or 1,3-aminophenols. The primary intermediates are oxidised by peroxides to give the colonred benzo-quinonediimines or monoimines, which react with the couplers to give indoamines or indophenols, e.g. (2.52) and (2.53), depending on the natnre and ratio of the reactants, as shown schematically in Fignre 2.20. ... 

The physical and chemical properties of dyes are very important for even coloring. First a hair dye should have comparable affinities for the roots, damaged areas, and tips. Second, the combined yellow-to-blue dyes used for shading must have similar properties so that color shifts will not take place when the hair is washed, for example. The importance of these problems is illustrated by the number of patent applications disclosing new, custom-tailored dyes [35] and suitable dye mixtures [42], The relatively good colorfastness and stability of some nitro dyes allow them to be used in oxidation hair dyes as well, especially for the shading of brilliant (mainly red) fashion colors. 

Permanent hair colors can be achieved with tint shampoos. The shampoo base is adjusted to an alkaline pH and contains oxidation dye intermediates. Before application, it is mixed with hydrogen peroxide or a hydrogen peroxide addition compound. In comparison with oxidation hair dyes, tint shampoos employ lower concentrations of base and oxidant. This suppresses the simultaneous bleaching process that occurs during dyeing (see Section 5.4.2). As a result, damage to the keratin in hair is diminished, but the uniform coloring action is lost. 

Early oxidation hair dyes were used in solution form these have been replaced by cream- or gel-based formulas. The oil-in-water emulsions commonly used can be supplemented with auxiliary ingredients, such as polymers to improve combing ability, as well as other conditioning additives. Extensive patent literature is available on this point [35], Gel formulations may be based on alcoholic solutions of nonionic surfactants or fatty acid alkanolamide solutions, which form a gel when mixed with the oxidant. The type (emulsion or gel) and the basic composition of the preparation strongly influence dyeing [47], Different base formulations with the same dye content yield varying color depths and shading due to the distribution of the dye between the different phases of the product, interaction with surfactants, and diffusion from the product into the hair. 

Hair dyes must meet a number of conditions related to their end use. Color can be assessed by colorimetry [49], The limits of precision are set by the substrate on which the measurement is performed. Studies on test subjects are difficult because of the uneven natural hair color and the background color of the scalp. Tresses are hard to prepare at a constant quality level. Measurements on wool cloth give reproducible results, but for oxidation dyes the shades are not identical to those produced on hair. Colorimetric methods are therefore useful only for comparative measurements on the same object, for example, in lightfastness tests. Because hair must be redyed after four to six weeks due to growth, the fastness required of hair dyes is generally less than that needed for textiles. However, stability is still a problem with many indo dyes (see Section 5.4.3). Some of them... 

Lightening or removal of hair color without structurally damaging the hair shaft is a difficult process. Oxidizing agents, including hydrogen peroxide,... 

About 80% of the dyes used in hair coloring are known as oxidation hair dyes.49-50 The remaining 20% of the available hair dyes... 

When used alone, the primary intermediates give a quite limited shade range following oxidation on hair. To enhance the range of available hair colors, the primary intermediates are oxidized in the presence of suitable couplers ) Whereas most couplers do not... 

Permanent hair colors contain an oxidizer (usually 6% hydrogen peroxide) and a dye intermediate (p-phenylenediamine, resorcinol, aminophenols along with water, ammonia, glycerin, isopropanol, and propylene glycol). Semipermanent hair colors contain propylene glycol, isopropanol, fatty acids, fragrance, alkanolamines, and dyes. Some Grecian hair formulations contain lead in the form of lead acetate. 

Chemoxide. [Chemron] Alkyl amine oxides foam booster, vise, builder, wetting agent for mild cosmetics, hair colorants, gels, permanent waves. 

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