64 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Figure 4. Scanning electron micrograph of hair surface before treatment with diperisophthalic acid. Mid- length region of control hair.

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