Permanent Waving of Human Hair

Nessler is reputed to be a key figure in the invention of the permanent wave during the early 1900s [124]. The first permanent waves were concentrated solutions of alkali (5 to 15%) or alkaline sulfites [124,125] that were reacted with hair at elevated temperatures. In these treatments, high temperatures were achieved by using either curling irons, chemical heating pads, or electric heaters [126]. 

Current permanent waves are vastly superior to the early hot waves and do not require elevated temperature, thus the designation cold waves. Cold waves became successful during World War II and have not changed substantially for nearly 40 years. These products are based on mercaptans or sulfites, the most common of these being thioglycolic acid, which is generally employed at a concentration of approximately 0.6 N and a pH of 9 to 9.5. 

The sulfite wave has made a comeback, with more than one manufacturer now offering a sulfite-based product. Sulfite waves employ a pH near 6 and a hydrogen peroxide neutralizer. This type of wave generally claims to provide a wave that does not frizzle the hair (i.e., is gentle to your hair) 

Cold Wave Formulations and Making Cold Wave Products 

A typical thiol permanent wave will consist of two compositions. The first a reducing solution, often called a waving lotion, will be of a composition similar to that in Table 3-2. 

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The chemistry of the reactions of permanent waves with human hair involves reduction of disulfide cross-links and molecular shifting by stressing the hair on rollers followed by reoxidation. These reactions produce extensive changes to the tensile properties of the fibers, both during reduction and even after reoxidation. 

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. 

In spite of the fact that research on permanent waving has decreased over the past several decades, significant findings have been made within the past 10 years. For example, Wortmann and Kure [1,2] have developed a model and recently extended it to show that the bending stiffness of reduced and oxidized fibers controls the permanent waving behavior of human hair and that the cuticle plays a role in permanent waving. Further, they have shown not only that the cuticle functions as a barrier to reduction but also that its stiffness may contribute to fiber set. 

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%). 

The objective of these density experiments was not to determine the absolute density of human hair, which is elusive [88], but to determine the relative density of human hair and wool fiber and the influence of damaging cosmetic treatments on this important property. The results of these experiments confirm the conclusions of several others [75, 89] the densities of human hair and wool fiber are similar, and there is no appreciable change in the density of human hair from permanent-waving or bleaching treatments. 

SAFETY PROFILE Poison by intravenous and intraperitoneal routes. Moderately toxic by ingestion. A human skin irritant. This material yields hydrogen sulfide on decomposition. A death has been attributed to the absorption of toxic decomposition products from the use of this material in a hair permanent-waving solution. When heated to decomposition it emits toxic fumes of SOx and Na20. See also SULFIDES and MERCAPTANS. 

What happens in a permanent wave Permanent-wave lotions are designed to penetrate the scales of the cuticle, the outer layer of the hair shaft. The lotions work because they affect the structure of the proteins that make up the hair. The amino acid cysteine, which contains an atom of sulfur, is found in human hair protein. Sulfur atoms in neighboring cysteine molecules within the hair protein form strong, covalent, disulfide (S — S) bonds. This cross-linking between cysteine molecules holds the strands of hair protein in place and affects its shape and strength. 

Nineteen amino acids in human hair have been studied for possible modification during permanent waving (i.e., all the amino acids of Table 2-1 except tryptophan and citrulUne). Significant decreases in cystine (2 to 14%) and corresponding increases in cysteic acid [1,10] and cysteine [1] have been reported for human hair that has been treated either on the head by home... 

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. 

Like feathers and hair, wool consists mainly of keratin. This polypeptide contains L-cystine which is the oxidised (disulfide) form of L-cysteine. The former acts as a cross-link which determines the crimped nature of wool. In human hair this process is, of course, carried out reversibly in permanent waving ... 

Human head hairs were obtained from seven different individuals. Some of the subjects provided multiple samples of hair treated in different ways. Hair samples that had been permanently waved, dyed and bleached were used in order to determine if these treatments had an effect on the deterioration of the hairs. All hair samples were cut from the donors heads consequently, roots were usually absent from the hairs. 

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