Bleaching Human Hair

The objectives of this chapter are to describe bleach product compositions and their formulation and to review the chemistry of both chemical and photochemical bleaching (i.e., the oxidative degradation of hair pigments and the accompanying oxidative degradation of the proteins of human hair) and to describe the chemical nature of bleached hair. 

---

Diluted H2O2 (between 3% and 8%) is used to bleach human hair when mixed with ammonium hydroxide, hence the phrase "peroxide blonde". 

Hair. Hydrogen peroxide is the most satisfactory bleaching agent for human hair. Solutions containing 3—4% hydrogen peroxide, available from dmg stores and supermarkets, are commonly used. In beauty shops, more rapid bleaching is desired and a 5—6% solution is used. Ammonium hydroxide is usually the source of aLkaliuity in both systems (see Cosmetics Hair preparations). 

Hair. Hydrogen peroxide is the most satisfactory bleaching agent for human hair,... 

In spite of the importance of bleaches in oxidation dyeing, very few technical improvements apart from formulation aspects have occurred recently in this field. The selective adsorption of metal ions [21], especially of iron(n) salts [22], on melanin has been proposed for gentler bleaching of human hair. This process has achieved no more acceptance than the use of peroxocarboxylic acids or their precursors, which are important as bleaching intensifiers in textile bleaching. 

Hoting, E. and Zimmermann, M. (1997). Sunlight-induced modifications in bleached, permed or dyed human hair. /. Soc. Cosmetic Chem. 48, 79-91. 

Black corals that consist of a homy material can be bleached with hydrogen peroxide - in much the same way as can human hair, which also consists of a homy material. The resulting coral resembles golden corals, which are more rare than black. The effect does not penetrate to the core, but it is very convincing, and thus difficult to identify without cutting into the material. 

Unaltered human hair is hair that has not been chemically modified by treatment with bleaches, permanent waves, straighteners, or hair dyes. Numerous publications [6,12-27] describe results of the amino acid analysis of unaltered human hair. Table 2-1 depicts the structures for 21 amino acids that have been identified in human hair. Cysteic acid and other amino acids, derived from those amino acids of Table 2-1, are also present in either weathered or cosmetically altered hair, see Table 2-2. Table 2-3 summarizes results from several sources describing quantitative whole-fiber analyses of these 21 amino acids. These same amino acids are classified according to functional group in Table 2-4. 

As a result of these large compositional differences, these two layers of the cuticle can be expected to react differently to permanent waves, bleaches, and even water and surfactants. Raper et al. [72] have described a method to determine the cuticle composition from endocuticle of chemically treated wools. Such a procedure would be valuable to evaluate changes in the endocuticle of cosmetically modified human hair. 

Reactions of the Proteins of Human Hair with Bleaches Chemical Oxidation of the Disulfide Bond... 

Since the bleaching of human hair is carried out in an aqueous alkaline oxidizing medium, hydrolysis of the cystine oxide intermediates (Figure... 

Zahn and co-workers [2], using two-dimensional gel electrophoresis, separated up to 62 isolated protein spots from human hair. From the fluoro-gram of bleached hair, these scientists identified cystine oxides (monoxide and dioxide). Although the exact quantities of these intermediate oxidation products versus cysteic acid were not reported, the quantities were indicated to be small relative to the cysteic acid content [2]. 

To summarize, sulfonic acid is the principal established end product of the oxidative cleavage of the disulhde bond from the chemical bleaching of human hair with current hair bleach products [3,9]. The mercaptan content of bleached hair is lower than that of unbleached hair [4], The intermediate oxidation products of cystine (i.e., the disulhde monoxide, dioxide, trioxide, and tetroxide) do not exist as signihcant end products of hair bleaching using today s commercial bleach products [3,6,9]. Nevertheless, evidence has been presented demonstrating low levels of cystine oxides in bleached hair [2],... 

Oxidative bleaching of human hair on live heads provides similar results for the tensile properties. Robbins examined both the wet and dry tensile properties of frosted and nonfrosted hair fibers from the same person (Table 8-3). Except for the resilience ratio, the loss in dry tensile proper-... 

We have determined the density of human hair in solutions of benzene-carbon tetrachloride by the method of Abbott and Goodings [86]. The density of chemically unaltered hair at 60% RH varied from 1.320 to 1.327, depending on lot (dark brown European hair from DeMeo Bros., New York, and three samples taken from heads of volunteers). The density of our wool control was 1.320, identical with one lot of hair. Permanent waving did not change the density of hair. Bleaching (approximately 25% disulfide rupture) increased it, but only by 0.45%). 

---