DAMAGE TO HUMAN HAIR 65 Figure 5. Scanning electron micrograph of hair surface after one treatment with diperisophthalic acid. and degradation of the cuticle induced by these treatments depicted in the light micro- graphs is reminiscent of the Allworden reaction (5), a reaction of hair fibers with chlo- rine water that degrades human hair. Decreases in the wet tensile properties of hair, in the vicinity of 25 treatments, with this reagent (Table I) are attributed primarily to the degradation of disulfide bonds (in the cortex). Alexander et al. (6) showed that the wet tensile properties of wool fibers decrease in a manner that is directly related to the disulfide content, through 60 percent disulfide rupture. Robbins (7) found similar effects for bleached human hair fibers. The fact that no significant changes in the wet tensile properties were detectable after three and six treatments with this system, yet gross alterations were observed throughout the cuticle layers, is in agreement with the hypothesis that disulfide bonds in the cortex and not in the cuticle are primarily responsible for the wet tensile properties of human hair fibers. Microscopic observations were also made in the dry state via SEM, on a midsection of

66 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Figure 6. Scanning electron micrograph of hair surface after three treatments with diperisophthalic acid. the control hair (see Figure 4). Contrast this SEM to those taken from hair fibers after one and three treatments (Figures 5 and 6, respectively). After one treatment, clear changes are observable at the cuticle scale edges and the scales appear thinner than for the untreated control hairs. These observations are confirmed by Figure 6 (after three treatments), which additionally shows clear longitudinal ridges and valleys in the scales, indicative of gross damage to the scales. This damage probably results from degradation and dissolution of proteins from within the cuticle scales. Decreases in the dry tensile properties (Table 1) are attributed primarily to degradation of peptide bonds (6). The fact that no decreases in dry tensile properties were observed through six treatments, yet extensive cuticle degradation was observed throughout the cuticle (Figures 3 and 6), suggests that peptide bonds in the cortex are primarily re- sponsible for the dry tensile properties of human hair. Furthermore, the fact that both the wet and the dry tensile properties did not change