60 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS damage throughout several cuticle layers, with no detectable changes in the tensile properties. These observations support the above hypothesis, that the cuticle in human hair has little involvement in the tensile properties of human hair. It also supports the two-phase model of Feughelman (4) that describes the mechanical behavior of human hair in terms of cortical structural components. EXPERIMENTAL The keratin fibers used in this study were either from 10-inch dark brown hair (DeMeo Brothers, New York) or from hair treated on heads of individuals, all purported to be cosmetically unaltered by permanent waves, bleaches, dyes, and straighteners. Thirteen grams of Suprox (PPG Industries, Inc., consisting of 15.4% diperisophthalic acid incapsulated in hydrated magnesium sulfate and sodium sulfate) and 6 gm of sodium carbonate were mixed together in 81 gm of a solution consisting of 3 gm sodium lauryl sulfate in 78 gm of aleionized water. Approximately 100 gm ooe this formulation was used for an average female head, in the experiments performed on heads. For the experiments on tresses, approximately 5 gm of the above prepared for- mulation was used on 2-gm tresses. Fibers were selected at random, each mounted on tabs at a gauge length of 5 cm. After the fibers were conditioned, either in water for 30 min or at 60 percent relative hu- midity for 24 hr at 24øC, they were stretched to break on an Instron Tensile Tester. The rate of extension was 0.5 cm/min. The average of 15 to 25 hairs was used for each data point, and several parameters of the tensile curves were compared. Small bundles of hairs were sectioned using a Hardy microtome, and the small hair cross sections, in water, were examined under a light microscope. Other fibers from these same treatments were selected at random, coated with gold, and examined with an Amray 1645 scanning electron microscope. RESULTS AND DISCUSSION The oxidant used in this study, diperisophthalic acid, is a relatively large molecule compared to hydrogen peroxide, and therefore its diffusion rate through hair must be considerably slower than that of peroxide. Nevertheless, this species is capable of rapid oxidation of the disulfide bond, provided it comes in contact with that bond. Human hair tresses were treated with this reagent as described in the experimental section for 10-min treatment times, and fibers were taken from the tresses, examined microscopi- cally, and tested for wet and dry tensile properties. Table I summarizes the tensile effects produced by this reagent. For the wet tensile properties, no significant differences were observed between untreated control fibers and treated fibers through nine treatments. But after 25 treatments, a significant decrease in the wet tensile properties was observed. For the dry tensile properties no significant changes were noted through six treatments. However, at nine treatments and beyond, significant decreases in the tensile properties were observed. Fibers from these treatments were examined further by making cross sections and exam-

DAMAGE TO HUMAN HAIR 61 Table I Tensile Properties of Diperisophthalic Acid-Treated Hair No. of Force to break Force to break treatments (Wet: %/•) (Dry: %/•) 3 +2.0% In] -0.3% In] 6 + 0.5 % In] - 1.8 % In] 9 - 1.6% In] - 3.5%** 25 - 12.5%** -9.5%** ** Indicates a significant difference at the alpha ---- 0.05 level. [n] Indicates no significant difference. ining the cross sections under a light microscope. Figure 1 depicts control fiber cross sections in water. The control hairs display little cuticle swelling and no separation of cuticle cells. Figure 2 depicts hair fiber cross sections in water after three treatments with diperisophthalic acid. Note the swollen cuticle region and the separation of cuticle cells relative to the controls. Figure 3, depicting hair fibers in water after six treat- ments, shows even greater swelling and separation of cuticle cells. The gross swelling Figure 1. Cross sections of cosmetically unaltered human hair in water (untreated control hairs)