UV DAMAGE ON GRAY HAIR 111 4.5 3.5 2.5 2 1.5 0.5 [3DL EIDb I•IDE 1 0.71 0.72 # 2, CATC 3,89 2.94 . # 3, OMC Brown Hair Sample 4.45 3.58 . # 4, SLS Figure 3. Change in color index values of brown hair tresses after UV irradiation. CHANGE IN TENSILE STRENGTH The changes in both the average Young's modulus and stress-to-break of gray hair samples after 15 days of UV irradiation are presented in Figure 5. It is readily seen that after 15 days of UV irradiation, hair fibers from gray hair tresses 2, 3, and 4 retained 94.6%, 87.7%, and 76.6% of their initial Young's modulus, and 92.7%, 85.4%, and 78% of their initial stress-to-break values, respectively. All of these reductions in tensile strength indicated that the cortex of the hair fiber was damaged and that some portion of the disulfide bonds, hydrogen bonds, and salt bridges were likely modified. The above results clearly demonstrated that CATC helped to maintain the tensile strength of hair. CHANGES IN DYNAMIC CONTACT ANGLE Changes in the average dyanmic advancing contact angles of gray hair fibers after UV irradiation are presented in Figure 6. It is readily seen that the average advancing contact angles of hair fibers from tresses 3 and 4 decreased dramatically, which indicates that the characteristics of the hair surface were changed from hydrophobic to hydrophilic because of the surface damage. This increase in the hydrophilicity and wettability of the hair surface may be partially attributed to the loss of 18-MEA and other fatty acids on the hair surface (10). In contrast, only the hair fibers treated with CATC maintained their

112 JOURNAL OF COSMETIC SCIENCE i~10 y = -0,758x -15 -20 -25 -30 -35 -40 0,00 5,00 10,00 15.00 20.00 25.00 30.00 35.00 40.00 45,00 Extension of Length {%} Figure 4. Plot of length extension vs. contraction of cross-sectional area of hair fibers. 50.00 L o 110 -• ............................................................................................................................................................................................................................................ lOO 9o 80 70 60 50 lOO -- Stress-to-Break lOO , [] NO UV [] CATC • OMC 94.6 [] SLS ........ ___ Young's Modulus Figure 5. Changes in stress-to-break and Young's modulus after UV irradiation.