ALKALINE PEROXIDE TREATMENT INDUCES ACQUIRED UNRULY HAIR 265 structure. Figure 5 depicts the ratio of the Young’s modulus of each macrofi bril to the average Young’s modulus of the macrofi bril on the paracortex-like structure on the con- cave side (for curly hairs for straight hairs, the left side was arbitrarily chosen). Figure 3. Comparison of spatial distribution of the two types of cortical cells among four types of hairs. Spatial distribution of the two types of cortical cells (black: orthocortex-like structure white: paracortex-like structure) on the concave side (left) and convex side (right): (A) in virgin straight hair, (B) in bleached straight hair, (C) in virgin curly hair, and (D) in bleached curly hair. Figure 4. AFM images on cross section of bleached curly hair in water. (A) Height image. (B) Phase images (left: concave side right: c onvex side). (C) Young’s modulus images corresponding to the phase images above.

JOURNAL OF COSMETIC SCIENCE 266 Figure 5A reveals that Young’s modulus of macrofi bril in virgin straight hairs had almost the same value throughout, without regard to the type of cortical cell or whether the scan area was on the left or right side. Comparison of Figures 5A and B reveals that Young’s modulus of macrofi brils was lower on the orthocortex-like structure than on the paracortex-like structure. Macrofi brils on the paracortex-like structure were damaged by bleach treatments furthermore, macrofi - brils on the orthocortex-like structure were severely damaged, as reported by Kitano et al. in 2008. Figure 5B also confi rmed that the intentional division of the straight hair into left and right sides was not meaningful, as expected. Importantly, comparison of Figures 5A and C revealed that in many curly hairs, Young’s modulus of macrofi brils of cortical cells on the convex side was lower than on the concave Figure 5. Comparison of Young’s modulus of four types of macrofi brils among four types of hairs. Ratio of average Young’s modulus of macrofi brils on the paracortex-like structure on the concave side to that of Young’s modulus of macrofi brils on the concave side (left) and the convex side (right): (A) in virgin straight hair, (B) in bleached straight hair, (C) in virgin curly hair, and (D) in bleached curly hair. Statistically sig- nifi cant difference compared to the average of Young’s modulus of the macrofi bril on the paracortex-like structure on the concave (left) side by using two-tailed T test (n = 20, α = 0.05).