MORPHOLOGY OF ASIAN AND CAUCASIAN HAIR 331 a b C Figure 5. a: Original SEM image of hair surface. b, c: The cuticular outline between the two arrows was traced using an image analyzing program, Image-Pro® Plus Version 4.0, at a minimum (b) or maximum (c) smoothing level, as indicated by the white line. The length of the traced line was measured and defined as Lmin and Lmax• respectively. MEASUREMENT OF CUTICULAR ELASTICITY Hair fibers were cut from near the scalp of seven subjects for each Asian and Caucasian, and embedded in epoxy resin (TAAB). Subsequently, the resin was cut with an ultra­ microtome Ultracut EM UPR (Leica, Tokyo, Japan) to expose the hair cross sections. The elasticity of exocucicle and endocuticle were measured using a nanoindentation tech­ nique (6) with a NanoScope Illa Multi Mode AFM (Digital Instruments, CA). Silicon tips (NCH type, Veeco Instruments, CA) were used, and the spring constant was measured by using the Cleveland method (7). This was performed using the micromanipulator method: A tungsten sphere deposited on a clean, dry surface was picked up by a glass capillary and attached to a tip. The resonant frequency of the cantilever was measured and then the sphere was removed from the tip. The mass of the tungsten sphere can be estimated from its diameter and known density. The resonant frequency, u, depends on added mass, MJ according to M = k(2 m,r2 -m* where m* is the effective mass of the cantilever. Thus, if a series of different masses are attached, a plot of M vs 1/u2 yields a straight line, of which the slope (m) can be used to determine the spring constant: k=4,r2 · m For all measurements, a constant applied force, defined as the product obtained by the multiplication of the cantilever deflection and spring constant, of 4 µN was used. Twenty-five indents were made on each cross section. All measurements were performed with the same cantilever at 1 µm/s. From the elasticity value of each indent point, it was found that the elasticity was relatively low on the inner half of each cuticle cell (nearer the center of the hair) and that

332 JOURNAL OF COSMETIC SCIENCE the elasticity was relatively high on the outer half of each cell. This correlates with the accepted bilayer structure of the cuticle cell, such that the former is regarded as the endocuticle, while the latter is regarded as the exocuticle. Although it is possible that the A-layer may be included in the latter, we have found the elasticity value of the A-layer (unpublished results) to be much higher than the values obtained for the exocuticle in the present study, and therefore this possibility can be excluded. The elasticity of each exocuticle and endocuticle was calculated according to the Sneddon theory, using the method described by Parbhu et al. (6). The shape of the end of the tip was assumed to be parabolic, with an approximate 20-nm diameter of curvature. The Poisson ratio was defined as 0.4, according to the value of common polymers. DAILY GROOMING TREATMENT As a simulation of daily grooming treatments occurring over three months, hairs bleached once and shampooed, conditioned, and blow-dried ninety times were com­ bined. This combination was repeated four times. After the completion of each combi­ nation treatment, ten fibers were taken from each hair tress. Two cross sections were exposed for each fiber, and these were observed by SEM. The number of cuticle layers was counted at four points in each cross section. RESULTS AND DISCUSSION STRUCTURE OF HAIR CUTICLE The number, thickness, interval, and tilt angle of the cuticles of both races are shown in Figure 6 (a-d), respectively. The measured values are shown in Table I. In all cases there were statistically meaningful differences at the 99% confidence level as determined by t-test, and therefore we conclude: • Asian hair has more cuticles than Caucasian hair (Figure 6a). • Asian hair has thicker cuticles than Caucasian hair (Figure 66). • The interval of cuticles is narrower for Asian hair than for Caucasian hair (Figure 6c). • The surface inclination of Asian hair is steeper than that of Caucasian hair (Figure 6d). EXTENDED HAIR SURF ACE Typical extended Asian and Caucasian hairs are shown in Figure 7a and 76, respectively. Both types of hair were damaged by the extension process, and some cracks were found ( .J, in Figure 7). In addition, the damage characteristics for each race were observed. In the case of Asian hair, it seemed that whole cuticle cells lifted up and the outlines of the cuticular edges were relatively smooth. In comparison, the liftup of Caucasian cuticles was less and the outlines of the cuticular edges were rougher. Measured roughness values of the cuticular outlines are shown in Figure 8. The values were similar for Asian and Caucasian cuticles prior to extension after extension, however, the values were increased in both cases, and it was particularly remarkable in the case of Caucasian hair. In addition, a lot of deposits, collapsed small fragments, and delamination within the