j. Cosmet. sci., 54, 353-366 (July/August 2003) Influence of internal structures of hair fiber on hair appearance. III. Generation of light-scattering factors in hair cuticles and the influence on hair shine MASAYUKI OKAMOTO, RYOKO YAKAWA, AKIRA MAMADA, SHIGETO INOUE, SHINOBU NAGASE, SATOSHI SHIBUICHI, EMIKO KARIYA, and NAOKI SATOH, Kao Corporation, Analytical Research Center, 1334 Minato, Wakayama-shi, Wakayama 640-8580 (M.O., R.Y., S.I.), and Kao Corporation, Hair-Care Research Laboratories, 1-3, Bunka 2-chome, Sumida-ku, Tokyo 131-8501 (A.M., S.N., S.S., E.K., N.S.),Japan. Accepted for publication December 20, 2002. Based on a presentation at the 2001 IFSCC International Congress, Taipei, Taiwan, September 17-19, 2001. Synopsis The effects of thermal treatments on hair fiber induced by blow-drying have been investigated. It was found that the hair shows whitish and powdery appearance after heat drying, especially when dark hair is rapidly dried from a wet condition. For all kinds of hair, the appearance of numerous glittering speckles was confirmed on the cuticle surface by optical microscopic observations. SEM images of hair transverse and longitudinal sections with glittering speckles revealed that the splitting of cuticle layers generated by blow-drying occurred not only at the outermost parts of cuticle cells but also at the inner parts of the cellular interfaces. The release and uptake of moisture through fiber surfaces induces deformation of cuticle cells, probably because of anisotropic swelling or drying of the cells. The cuticles with glittering speckles are found to be fragile and are easily damaged in combination with other mechanical stresses such as combing force. Furthermore, the authors have found an efficient system for both improving hair shine and preventing cuticle damage caused by the blow-drying/combing process. INTRODUCTION The structure of human hair is a highly organized stratum that is very resistant to external stimuli. However, morphological changes can occur through daily hair care routines, chemical treatments, exposure to UV-light, and other stresses. Hair damage leads to a change in not only the physical properties of hair, by becoming harsh, stiff, weak, and brittle, but also in optical properties such as shine. Hair shine is one of the largest concerns of consumers, and as a result, numerous studies regarding hair shine have been conducted. Although most of the studies discuss the optical properties at the hair surface, we have found that structural changes occur in the internal hair fiber 353

354 JOURNAL OF COSMETIC SCIENCE through daily hair care routines. These actions in the daily hair care routine influence hair appearance, such as light scattering from the cuticle cell, cortex, and medulla tissues (1-4). In this paper, the effects of blow-drying treatments on human hair have been investi- gated. As is well known, blow-drying with a hair-dryer is nowadays one of the common customs in daily life, and thus structural changes occurring in the hair cuticle by blow-drying have been reported (5-8). Studies regarding cuticle damage have been conducted from the viewpoint of both thermal transition (5-7) and changes in the moisture content (8) in hair keratin. We have made a further examination of hair cuticles, focusing on structural changes caused by blow-drying, and discovered the generation of splitting spaces between the cuticle layers. This phenomenon is considered to occur frequently in the daily hair care routine and influences both hair shine as well as the cuticle degradation process. The authors present an analysis of the generation mechanism of the interlayer spaces of cuticle layers through blow-drying and the effect of this phenomenon on hair cuticle damage. EXPERIMENTAL MATERIALS AND METHODS The fibers used in this study were chemically untreated hair of Japanese women in the 20-to-40 age range. In order to condition hair moisture, the fibers were kept overnight at a constant temperature and humidity. A blow-dry treatment was administered using a hair dryer with a heated air blower for 30 seconds. The hair samples were heated at 70øC by the blow-dry treatment. The amount of scattered light from the interlayer space of the cuticle cell was evaluated using optical microscope views of the fibers at a low magnification (x50). We classified the hair fibers into five grades according to the amount of glittering speckles they contained, and used these grades as the standards. The evaluation was performed by comparing these standard sheets as references. Evaluation of light scattering by blow-drying was also conducted for the fibers treated with an aqueous solution of malic acid (MA: 4 wt%)/benzyloxyethanol (BEE: 10%)/15 % ethanol at 25øC for an hour. The measurements of hair moisture before and after the MA/BeE treatment were performed by conventional Karl Fischer method. The hair fiber was introduced into 50 rnl of the solvent to be used as the azeotrope formula and distilled until most of the solvent had been collected. A small excess of Karl Fischer reagent was added to the distillate, and the back was titrated with water in methanol. The hair cuticle damage caused by hair care routine with blow-drying was evaluated. Each hair care cycle consisted of shampooing/rinsing and combing during blow-drying, and the number of applied cycles was 150 times. The hair damage was evaluated by means of counting the total number of cuticle layers before and after cycles with the help of the FE-SEM observation of the hair transverse sections. A total of ten fibers per each sample was analyzed. In order to evaluate the protection effect of the malic acid (MA)/ BeE treatment against hair damage, hair fibers were treated with a MA/BeE solution after rinsing each time.