j. Soc. Cosmet. Chem., 44, 221-234 (July/August 1993) Light scattering and shine measurements of human hair: A sensitive probe of the hair surface CHARLES REICH and CLARENCE R. ROBBINS, Colgate-Palmolive Research Center, 909 River Road, Piscataway, NJ 08854-I343. Received January 29, I993. Synopsis In this paper, an instrumental method for measuring hair shine is presented and shown to exhibit excellent correlation with a large series of subjective evaluations of shine. In addition to providing shine values, the light-scattering methods developed are shown, in many cases, to provide a sensitive means of following changes to the hair surface, including deposition (soiling), particle removal (cleaning), and even interactions on the fiber surface. Employing the developed methods, the effect of washing hair tresses with a series of commercial shampoos is investigated. The effects examined are shown to fall into three classes: Shampoos without highly substantive ingredients left hair in its cleanest and shiniest state. Shampoos containing ingredients substantive to hair (polycationics and soap) left deposits on the fiber surface and dulled the hair. The worst dulling was observed when particles deposited on the hair from one shampoo formed a complex with particles contained in a second product. INTRODUCTION Shiny hair is consistently cited by consumers in panels and surveys as one of the most desirable of cosmetic attributes. As a result, much effort has been expended in recent years to understand the physical phenomena that give rise to shine and also to quantitate this desirable hair attribute. The most effective means described in the literature to study hair shine has been the use of a goniophotometer to measure light scattering by hair fibers (1-4). Goniophotometric techniques have been used by the authors of references 1-4 to relate light-scattering patterns to hair morphology and also to develop formulas relating goniophotometric data to hair shine. Unfortunately, the bulk of the effort in the above studies has been concerned with explaining the light-scattering patterns only cursory efforts were made to relate calcu- lated shine values to panelists' subjective evaluations. In addition, little effort was made to systematically apply the methods developed in these papers to problems related to hair care. In this paper, a large series of subjective evaluations of hair shine is reported and shown 221

222 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS to exhibit excellent correlation with a formula developed to calculate hair shine using goniophotometric measurements. In addition to providing a quantitative measure of shine, the light-scattering methods developed in this work are shown to provide a means of following changes to the hair surface, including deposition (soiling and buildup), removal of particles (cleaning), and even interactions at the fiber surface. Single-fiber techniques are presented and shown to provide a rapid, qualitative means of determining the effects on hair fibers of various treatments. The results of shine mea- surements of tresses exposed to various treatments of interest are then shown to confirm and make quantitative the foregoing single-fiber results. Finally, the shine of hair tresses treated with various shampoos is measured and shown to be a function of the nature of the substantive ingredients found in particular sham- poos. The results in this paper show that light scattering can be used not only to obtain quantitative information about shine but that it can also serve as a sensitive probe of the hair surface, providing information difficult or impossible to obtain using other surface techniques. EXPERIMENTAL SHAMPOO EXPERIMENTS All tresses for shampoo experiments were prepared using three grams of human hair purchased from DeMeo Brothers, New York. In order to minimize scattering from the rear cuticle, only dark brown Oriental hair was used (1). For each comparison series, a minimum of three tresses was prepared for each shampoo treatment. In addition, three control tresses, treated only with 20% sodium lauryl sulfate (SLS) and representing "clean hair," were prepared for each series. In comparison experiments, succeeding tresses in a series received different treatments so that any particular treatment was staggered throughout the entire series. All tresses were subjected to five pretreatment washes with SLS, followed by five treatments with a test shampoo. In those cases where shampoo combinations were employed, five treatments with the first shampoo were followed by three treatments with a second. Pretreatment cycles were performed by immersing tresses for five minutes in 250 ml of 5 % SLS in a graduated cylinder. The tresses were then removed, rubbed by hand for two minutes, and then rinsed twice for one minute each in graduated cylinders containing 500 ml of deionized water. Treatment cycles were performed in the same manner as the above, except that a 2: ! tap water, shampoo solution was substituted for SLS, while tap water rather than deionized water was employed in rinses. Note that the tap water used in these experiments had a water hardness level of 80 ppm. SUBJECTIVE SHINE EVALUATIONS Subjective evaluation of tress shine was performed on groups of six tresses each, with