MORPHOLOGICAL CHANGES OF HUMAN HAIR 345 Furthermore, the in vitro method was successfully transferred into a real-life setting by analyzing the movement of women’s ponytails while walking on a treadmill (in vivo method). The results of both the in vitro and the in vivo methods show a consistent rela- tionship. Compared with pigmented hair, the “swing height” of ponytails with ≥5% nonpigmented hair fi bers decreases like the relative amplitude of the nonpigmented hair strands and the damping of both hair collectives (ponytails with ≥5% and nonpigmented hair strands) increases. The results of in vitro and in vivo measurements well refl ect the perception of women with the appearance of “gray” hairs. ACKNOWLEDGMENTS The authors wish to thank the KKD Hair Biophysics department of Dr. Sabine Babiel (Henkel AG & Co. KGaA) for assistance with the conduction of the fi ber diameter and tensile strength measurements. REFERENCES (1) C. Robbins, P. Mirmirani, A. G. Messenger, M. P. Birch, R. S. Youngquist, M. Tamura, T. Filloon, F. Luo, and R. L. Dawson, Jr., What wom en want—quantifying the perception of hair amount: an analysis of hair diameter and density changes with age in caucasian women, Br. J. Dermatol., 167, 324–332 (2012). (2) S. Nagase, Y. Kajiura, A. Mamada, H. Abe, S. Shibuichi, N. Satoh, T. Itou, Y. Shinohara, and Y. Amemiya, Changes in structure and geomet ric properties of human hair by aging, J. Cosmet. Sci., 60(6), 637–648 (2009). (3) M. C. Hindley, M. Yap, and H. Ugail, Measurement of hair dynamics via video image analysis, IFSCC Conference, November 2, 2011, Bangkok, Thailand. Figure 9. Box & whisker plot of the logarithmic decrement - pigmented and “gray” ponytails (n = 41). NP: nonpigmented, SE: standard error.

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