PROFILOMETRY OF HAIR 31 ¸ i o o direction of scan in mm Figure 4. Surface profile of a hair fiber (scan length 0.4 mm, axe-shaped stylus). The peaks seen originate from individual cuticular cells the mean distance between adjacent cells is 6-7 Ixm. This phenomenon is even more easily seen in Figure 5 where a different stylus is evalu- ated. A value of about 1 peak or cell/7 Ixm can be found (7). These results are compa- rable to electron microscopic findings revealing a mean distance between succeeding cuticular cells of 5-7 Ixm. Twenty hair fibers from one person were investigated, providing a mean value for Pc •1150 peaks/cm this value corresponds to a mean distance of 8.7 Ixm between suc- ceeding cells (Table I). Therefore, when using a scan length of 0.4 mm, the counted peaks result mainly from the thresholds or steps between adjacent cells. To determine if the roughness increases when moving from the root towards the tip region, we measured repeatedly a rather long (30 cm) and intact blonde hair with a scan length of 0.4 mm. An increase in roughness could be detected near the tip (Figure 6). This increase of Pc is a consequence of the difference in structure, possibly of the beginning of damage, which may be the reason for the better detectability of cell edges, i.e., increasing Pc at the tip region. In physical terms this means an increasingly loose attachment of cuticle cells to the cortex. The influence of scan length can be seen from Table II. Increasing scan length causes an increase in roughness parameters Rq, Rt, and Rz, but a decrease in Aq and Pc (Table II). The reason seems to be the increasing contributions from periodic or stochastic alter- ation of the hair surface which increase Rq, Rt, and R z. The decrease in Aq and Pc is caused by the loss of the fine structure determined by individual cells when increasingly longer segments of hair surface are scanned with constant data storage capacity.

32 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS o o • o o direction of scan in mm Figure 5. Chosen hair fiber (virgin brown hair, scan length 0.4 mm, pyramidal stylus). Reproducibility. Repeated scanning of defined segments of the hair surface showed almost constant values for roughness parameters (Table III). The direction of scanning was root to tip. Scanning in the opposite direction does change the surface, presumably because the stylus is lifting cuticular cells from supporting cell layers (Figure 7, left half of picture). Distribution of roughness values of hair fibers from difjSrent hair strands. Figure 8a shows the average distribution of the amplitudes of 14 scans (scan length: 10 mm) performed on Table I Mean Values of Roughness Parameters of 20 Hair Fibers Scanned at Different Distances From the Root (scanning lengths 0.4 and 1.25 mm) Scanning Distance length (mm) (mm) Rq Rt Rz hq Pc 7 0.4 • 0.201 0.83 0.44 4.4 1168 s 0.033 O. 152 0.095 0.457 69.9 1.25 • 0.373 1.51 1.08 4.7 1063 s 0.114 0.461 0.234 1.087 106.6 62 0.4 i 0.216 0.86 0.45 5.1 1144 s 0.037 0.125 0.064 0.579 97.5 1.25 • 0.411 1.60 1.08 5.0 1042 s O. 128 0.383 O. 177 0.876 133.4 mean-value. standard deviation.