34 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS -.--- ..... Figure 7. SEM photo of hair surface, scanned from root -- tip (whole section) and partially from tip -- root (left half) (-- & damaged surface). 14 hair fibers from one European female). The hair was cosmetically unaltered. The distribution of amplitudes is gaussian and in accordance with the profile shown in Figure 9. Counting the peaks in Figure 9, one finds approximately 11-12 peaks/4 mm, corresponding to an average distance between succeeding peaks of approximately 0.35 mm. The distribution of longer scans is skewed to the left (Figure 8b). Fourier analysis ofprojSles. Published results concerning growth speed of hair claim a rate of approximately 0.3--0.4 mm/day. Figure 10 depicts the results of a Fourier analysis. The average spectra show a distinct maximum at a frequency of 2.4 mm-•, corre- Rq = 3. 593 • • sk ....... 0.097 • •1• ....... 0.629 _o • scan-length 10 mm -I•.S '-8:S '-6:S '-4:S -2'.S' -C•.i ' I.S' 3.S 5.S ?.S 9.5 11.S profile-height in •m Rq = 4.191 • skewness = 1.267 • excess = 4.069 .......... ,,i : : : = ....... -10.5 -8.5 -6.5 -4.5 -2.5 -0.5 1.5 3.5 5.5 7.5 9.5 11.5 profile-height in •m Figure 8. Histograms and distribution function of Rq values of untreated hair fibers.

PROFILOMETRY OF HAIR 35 o o o o o o o direction of scan in mm Figure 9. Surface profile of a hair fiber (scan length 4 mm, axe-shaped stylus). sponding to a wavelength of 0.4 mm. If hair growth is regulated by circadian rhythms as the basal layer of the epidermis and other skin appendages are, then daily periodic changes of the fiber's diameter are possible. o o C O. O0 ß ß ß ß i i 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00 frequency (1/mm) Figure 10. Averaged amplitudinal spectrum of five hair fibers (brown, scan length 10 mm).