EFFECT OF AGE ON HAIR PROPERTIES 641 RESULTS CLINICAL INVESTIGATION From the sensory evaluation of hair luster by three evaluators, it was found that hair is more lustrous in young women than in elder women. Figure 2 shows the sensory hair luster scores of each decennial age group. Hair luster does not change signifi cantly up to the 30s, but decreases afterwards. Figure 3 shows the age dependence of the hair luster value, ΔL. The hair luster value varies widely from panelist to panelist however, it also decreases with age in general agreement with the sensory luster scores. This relationship is statistically signifi cant at a very high level (p = 3.0 × 10–11), and the index of determina- tion r2 is 0.176, indicating that 18% of the variation in the hair luster (ΔL) is explained by variation with age. Figure 2. Age dependence of hair luster from sensory evaluations. The hair luster was scored by sensory evaluations on 230 randomly selected Japanese females ranging from age 10 to age 70. All panelists had not had their hair permed in the last six months. Bars with an error bar: mean ± SD of each decennial age group. Asterisks *, **, and *** represent p 0.05, p 0.01, and p 0.001, respectively, obtained by Student’s t-test. Figure 3. Age dependence of the hair luster value, ΔL, obtained from digital photographs of the back of the head. The panelists are the same as in Figure 2. The defi nition of ΔL is described in Experimental. Solid line: result of linearization. Filled squares with an error bar: mean ± SD of each decennial age group.

JOURNAL OF COSMETIC SCIENCE 642 GEOMETRIC PROPERTY CHANGE BY AGING In Figure 4, the hair diameter (minor axis) is plotted against age. These are the averaged values of all hair fi bers sampled from a 7-mm × 7-mm area of the top of the head. Here, the hairs less than 5 cm in length are avoided so as not to count the newborn hairs. The hair diameter increases until the age of around 40, then decreases. This trend is consis- tent with the previous result on large numbers of Japanese females (3). This consistency suggests that the hair samples of this study are representative ones. In Figure 5, the el- lipticity of a cross section, defi ned by the ratio of the major to the minor axis, is plotted against age, showing that it has no dependence on age. The average value 1.28 indicates that the hairs are relatively round, compared to values for Caucasian and Ethiopian hair (1,14). As shown in Figures 4 and 5, the age dependence of both hair diameter and ellipticity does not correlate with the decrease in hair luster with age, meaning that the luster reduction with age does not arise from the changes in fi ber diameter or ellipticity. Figure 6 displays examples of magnifi ed photographs of the hair of three panelists and several hair fi bers randomly sampled from them. For the youngest (25 years old) panelist (a), the appearance looks smooth and the bright luster belt around the top of the head is Figure 4. Age dependence of minor axis of a hair cross section measured at 20°C and 65% relative humid- ity for 132 randomly selected Japanese females. Each point is the average of all the fi bers sampled from a 7-mm × 7-mm area of the top of the head for each panelist except for fi bers less than 5 cm in length. Solid curve: quadratic approximation. Filled squares with an error bar: mean ± SD of each decennial age group. Figure 5. Age dependence of the ellipticity of a hair cross section (major axis/minor axis). The panelists and measured hairs are the same as those in Figure 4. Solid line: result of linearization. Filled squares with an error bar: mean ± SD of each decennial age group.