1. Soc. Cosmet. Chem., 27, 571-578 (November 1976) Hair Body PATRICIA S. HOUGH, B. Sc., J. ELAINE HUE¾, B. Sc., and WILLIAM S. TOLGYESI, Ph.D.* Presented, May 29, 1975, SCC Seminar, St. Louis, Mo. Synopsis: HAIR BODY can be defined as the STRUCTURAL STRENGTH and RESIL- IENCY of a HAIR MASS. The definition conforms to the qualities assessed subjectively by hair cosmetic users. Five groups of fundamental parameters govern the mass structural strength of hair: hair density on the scalp, material stiffness, diameter, configuration of the fibers, and fiber-fiber interactions. The •otenti,al influence of hair cosmetics on hair body can be systematically analyzed by deducing their effects on these separate funda- mental parameters. It is proposed that current cosmetic products are effective in modify- ing hair body through only the last two factors: fiber configuration and fiber-fiber in•ter- actions. I. INTRODUCTION Terms like body and texture have gained greatly in their importance to hair cosmetics during the last few years. All major hair care product categories- shampoos, conditioners, setting aids, sprays, waves, bleaches, and dyes-tend to promise these characteristics to the consumer. The •erms have magic qualities because they represent much sought after properties and because they refer to some intangible characteristics which have not yet been defined. The aim of this paper is to offer a physical deftni- hon for hair body, analyze its component parameters, and discuss how differ- ent types of products assist in realizing it. II. D•scussIo• A. Definition Women tend to iudge hair body either by visual or tactile characteristics. According to the visual evaluation, a head of combed-out hair has body if it shows high elevation over the crown and significant lateral displacement at the sides, conversely, when the mass of hair closely follows the shape of the skull on the top and sides under its own weight, it is interpreted as lacking *Gillette Research Institute, 1413 Research Boulevard, Rockville, Maryland 20850. 571

572 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS body. In tactile evaluation, a mass of loose hair is usually compressed and relaxed, if it is firm and resilient, the rating is positive. While considerablc differences exist both in methods and ratings, a common characteristic can be found in all cases: hair body is associated with mass structural strength and resiliency. On the basis of this, it is proposed that: body is a measure of a hair lnass's resistance to, and recovery from, externally induced deformation. Some of the words of this definition nmst be emphasized. First, body always refers to a hair mass even if one may extrapolate to it from single fiber properties. Secondly, body is a quantitative characteristic and, therefore, the word measure must be included in the definition. Hair with no body means that some or all of the fttndamental parameters which contribute to the mass strength are present at low levels only. The above definition satisfies the characteristics which are judged by the visual method of body determination according to the following. The emerg- ing angle of hair fibers is high in relation to the skin. Consequently, the fibers would keep pointing in a substantially radial direction with regard to the skull in the absence of outside forces. The continuously acting external modifier is the gravitational force. Depending on the balance between structural strength and resiliency of the hair on one hand, and the gravitational load on the other, the hair mass may show more or less elevation bulkiness. The word bulkiness is used here in terms of its textile definition, meaning low structural density. In connection with the hand compression method of body evaluation, it is evident that strength and resiliency characteristics are appraised and, there- fore, it fits the above given definition for body as well. B. Component Factors in Hair Body The above definition equates body with the resilient strength of a hair mass under static and dynamic conditions. The resilient strength of any multicom- ponent engineering structure, which a hair mass is, is influenced by a number of independent parameters. In the most basic form, five such parameters need to be considered: fiber density on the scalp bending and torsional stiffness and resiliency of fibers fiber diameter fiber configuration and fiber-fiber interactions. 1. Fiber density on scalp: Fiber density is an important factor in modifying both structural volume and resiliency of hair mass over and at the sides of the head. When all other factors are equal, the volume of a fibrous mass is a linear function of the number of fibers in it. This correlation is satisfactory to indicate the direction of the influence, but it must not be applied quantita- tively to the elevation of hair over the head. The main reason is that the hair mass density decreases with increasing distance from the skin for any fiber density at the roots. The structural stabilization-originating from fiber-fiber