336 JOURNAL OF COSMETIC SCIENCE 800 exo/endo= 1.26 exo/endo= 1.41 700 600 500 endo exo endo exo ·u ·.;::: 400 300 200 100 0 Asian Caucasian Figure 10. Elasticity of exocuricle and endocuticle measured by the nanoindentation method. only in configuration but also in the hardness of the cuticular components, between Asian and Caucasian hair. Thus, the following hypothesis is suggested (Figure 11): Once Asian hair receives extension stress, the cohesion between cuticle cells (cell membrane complex), rather than the cuticle cells themselves, absorbs the stress and the cuticles lift up while keeping their original shape. When further stress is applied, Asian hair cuticles are broken at the cracks generated in the extension and fail as large fragments. In contrast, the relatively fragile Caucasian cuticles fall into small pieces when they receive such stress, especially with the splits generated in the fragile endocuticle or boundary between exocuticle and endocuticle. This failure is confined to the removal of small fragments even if stress is furthered. lift up complex Caucasian hair Figure 11. Assumed damage mechanism.

MORPHOLOGY OF ASIAN AND CAUCASIAN HAIR 337 Putting together this hypothesis and the structural features of higher cuticular edges and more inclined surfaces, there is a possibility that Asian cuticles can more easily receive physical stimuli and that the abrasion of the cuticles occurs more easily, compared with Caucasian cuticles. To confirm this, the damage to cuticles during daily grooming was then investigated. DAILY-GROOMING MODEL TREATMENT The number of residual cuticles remaining after grooming treatment is shown in Figure 12. This figure shows that cuticles are removed during the grooming process for both types of hair, but that in the case of Asian hair the cuticle removal proceeds faster. This result agreed with our expectations, as described in the previous section. CONCLUSIONS As a result of a comparative study of cuticle structures, it was found that Asian hair has more cuticles, which are thicker and more densely packed than Caucasian hair, as regards their small cuticular intervals. Furthermore, Asian cuticles are harder and the hardness of the cuticle cell components (exocuticle and endocuticle) is relatively even. This leads to an image of Asian hair having a more solid structure. In the case of extended Asian hair, however, cuticles lift up while keeping their original shape and are removed as large fragments. For extended Caucasian hair cuticles, small fragments are formed upon breakage. In addition, the fact that the edge of the cuticle is higher and the inclination angle of the hair surface is larger means that there is a possibility that Asian hair more easily encounters physical stimuli. Based on these results, it was assumed that Asian cuticles are more easily removed than 6 ---Asian 5 · - · Caucasian 4 (I) 3 "§ 4-- 2 0 -.._·.. f- - - - - -l-- (I) 0 0 2 3 4 Number of grooming cycles Figure 12. Number of residual cuticles after grooming treatment.