J. Cosmet. Sci., 69, 121–130 (March/April 2018) 121 Structural Analysis of Macrofi brils in a Human Permanent Waved Hair by Scanning Microbeam Small-Angle X-ray Scattering Measurements MAKI FUKUDA, YUKI MARUBASHI, TEPPEI NAWA, and REINA IKUYAMA, Beauty Care Laboratory, Kracie Home Products, Ltd., Yokohama 240-0005, Japan (M.F., R.I.), General Research & Development Institute, Hoyu Co., Ltd., Nagakute 480-1136, Japan (Y.M., T.N.) Accepted for publication March 27, 2018. Synopsis It has been experimentally shown that hair subjected to permanent wave treatment quickly changes into uncurled hair during daily hair-care activities. However, the mechanism of curl fallout has not been clarifi ed. In previous studies, the relationship between permanent wave treatment and disulfi de bonds in hair has been studied. Because permed hair falls out its waves without any chemical treatment, we focused on the hair microstructure rather than the disulfi de bonds. To examine the relationship between the hair curl shape and the intermediate fi lament (IF) organization in hairs, scanning microbeam small-angle X-ray scattering measurements were performed. It was found that in permed hairs, the IF orientation on the convex side of the curvature was different from that on the concave side. By contrast, for permed hairs with curl fallout, the IF orientation on the convex curvature side was not signifi cantly different from that on the concave side. Our fi ndings suggest that the curl shape of permed hairs is related to its anisotropic IF orientation between the convex and concave side of the curl, and control of this IF orientation will allow for effective reduction of curl fallout. INTRODUCTION A permanent wave (perm) can produce a hairstyle of one’s choice, and is familiar to people around the world. Basically, the perm treatment consists of two processes. In the fi rst process, the hair is wrapped around perm rods, and is treated with a reducing agent such as thioglycolic acid. These agent molecules break some of the disulfi de cross-links between polypeptide bonds in keratin, a protein present in hair. In the second process, the hair is treated with oxidizing agents while it is still wrapped around the rods. These agents reform the previously broken disulfi de bonds, but in such a way that it stabilizes the hair in their position around the rod. As a result, the hair exhibits waves even when the rods are removed. Disulfi de bonds in hair are, thus, central in these processes, and their role in permanent wave treatments has, therefore, been extensively studied (1–5). Address all correspondence to Teppei Nawa at teppei_nawa@hoyu.co.jp.

JOURNAL OF COSMETIC SCIENCE 122 However, many of these studies have dealt with the effect of permanent wave treatment on hair that was not wrapped around perm rods. For this reason, the relationship between hair curl shapes and disulfi de bonds may not have been fully understood. One factor is curl fallout: Curl fallout is the phenomenon by which, through daily hair care, the waves formed through perm treatment begin to deteriorate after roughly 1 mo. Although this issue of hairstyle maintenance poses problems to many, this phenomenon has not been studied, and the cause of curl fallout has not yet been clarifi ed. Because permed hair falls out its waves without any chemical treatment, we investigated changes in the microstructure of the hair rather than in disulfi de bonds. Because of recent developments of scanning microbeam small angle X-ray scattering (SAXS) technology, it is now possible to examine the inner microstructures of hair (6–11). The relationship between the shape of hair curls in naturally curly hair and the orienta- tion of intermediate fi laments (IFs) in the hair could, thus, be explored (12). The present study aims to clarify the cause of curl fallout, by investigating the relationship between the IF’s orientation and the curl shape of permed hair. To investigate the relationship, fi ve types of hair samples were prepared. The fi rst samples were hairs without perm treatment. The second samples were permed hair. The third samples were permed hairs repeatedly stretched. The forth samples were permed hair immersed sodium lauryl sulphate (SLS) solution. The Last samples were permed hairs stretched and immersed SLS solution. These samples were examined by scanning microbeam SAXS for structural analysis, and the relationship between curl shape and microstructure was discussed. MATERIALS AND METHODS CURL DIAMETER EFFICIENCY MEASUREMENTS Asian blended untreated hairs were used. Each hair bundle curl diameter was measured in a room where the temperature and humidity were adjusted to 25°C and 50% Relative Humidity (RH), respectively. The “curl diameter effi ciency” was calculated using the formula: Curl diameter effi ciency (%) = Rod diameter (mm)/Curl diameter (mm) × 100. Fifteen millimeter diameter spiral rods were used. The curl diameter effi ciency was deter- mined after the perm treatment and after each subsequent treatment (described in the following text). Each treatment was performed fi ve times, and average data was used for analysis. CHEMICAL TREATMENTS FOR CURL DIAMETER EFFICIENCY MEASUREMENTS Bleached hair. A bleach treatment was carried out for 35 min at 30°C using 1.0 wt% ammonia aq. and 3.0 wt% hydrogen peroxide aq. (pH 10.2) (⇒ bleached hairs). The scale of curl fallout was not suffi ciently large in virgin hairs after only a perm treatment to get reliable results. Hairs were, therefore, fi rst bleached and then permed, making the measured differences more prominent. We used bleached hairs as a control.