J. Soc. Cosmetic Chemists, 17, 769-787 (1966) Caucasian Hair, Negro Hair, and Wool: Similarities and Differences J. MENKART, Ph.D., L..1. WOLFRAM, Ph.D., and IRENE MAO, M.D.* Presented May 10, 196'6, New York City Synopsis--Caucasian hair, Negro hair, and Lincoln wool are compared in ternis of physical structure, mechanical properties, chemical composition, and rate of reaction with various re- agents. Several significant differences are found between wool and the two hair samples. The principal one is the extent of crosslinking, which is greater in the hair, as indicated by higher sulfur and cystine contents, and a higher proportion of the material found in the •-keratose fraction after oxidation. The heavier crosslinking is reflected in greater resistance to attack by hot acid and in slower reduction by thioglycolate or sulfite solutions. The main difference between Caucasian and Negro hair is in fiber geometry the Cau- casian fiber approximates a cylinder, the Negro a twisted oval rod. In their physical and chemical properties, the two fibers are very similar. I. INTRODUCTION Human hair, the wool of the sheep, and the hairs of the various goat species of textile importance (angora, cashmere) are closely related to each other morphologically, chemically, and physically. The simi- larities between them are, in most respects, so close that fiber investi- gators at one time developed the habit of treating them as almost inter- changeable. It became customary to employ human hair for studies of fiber mechanical properties directed to the understanding of wool the following quotation (1) is typical of numerous papers of the 30's and early 40's: "Human hair was selected for use in preference to wool * Harris Research Laboratories, Inc., Gillette Research Institute, Washington, D. C. 20007. 769

770 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS because of the greater uniformity of cross-sectional area of the fiber along its length." The practice came to be used as the realization grew that the various animal fibers differ significantly from each other in some important respects and that consequently caution needs to be exercised in applying results obtained on one fiber type to other keratin fibers. In Section II of this paper, differences between wool and hair are discussed published data are the main source of the survey. A narrower fiber comparison of interest to the cosmetic chemist is that between human scalp hair of different races. In this field, literature information is scanty except for data on fiber diameter and cross-sec- tional shape gathered in anthropological studies (2-5). A comparison of some chemical, physical, and mechanical properties of Caucasian and American Negro hair was therefore undertaken a standard wool (Lincoln) was examined at the same time. The results are reported in Section III. II. WOOL AND HAm In evaluating published comparisons of wool and hair, the problem of intraspecies differences comes into play. Most of the literature data are based on Caucasian hair, but in the case of wool many breeds and crossbreeds have been employed. The interbreed differences in most properties are probably minor, but in the review which follows the breed is specified wherever known. 1. Morphological Both wool and hair fibers have the same main morphological com- ponents-cuticle, cortex, and medulla. The cuticle, which consists of overlapping flat scale cells about 0.5/• in diameter, surrounds the fiber. In wool, the cuticle layer is 1-2 scale-cells thick in hair, 5-6 cells (6). The cuticle is more resistant to diffusion of reagents than the cortex (7) and more resistant to attack by chemical reagents, such as sodium sul- fide (8). It thus acts as a protective barrier to the body of the fiber against chemical as well as mechanical degradation. The greater resistance of human hair to chemical attack by many reagents (see below) is at least partly due to the thickness of the cuticular layer. The cortex of keratin fibers consists of spindle-shaped cells, oriented along the axis of the fibers. In wool, the cortex is divided into two com- ponents, differing from each other in their structure and reactivity:* * They are named (9) ortho- (the more reactive component) and para-cortex (the less reactive one).