219 INTERNAL STRUCTURE CHANGES OF EYELASH INDUCED BY EYE MAKEUP 600 times by changing the rotation angle by 0.3°—step to cover 180°. In the case of the typical measurement condition with the diameter of the hair sample of 100 μm, more than 1000 points are required for each transversal scan with 100 nm pitch. Therefore, totally more than 600,000 scan points (1000 transversal scan × 600 rotational scan) are required for one CT measurement. In such a measurement condition, it takes approxi- mately 30 min for a CT scan. STRUCTURE ANALYSIS OF RECONSTRUCTED EYELASH IMAGE Shape and size of eyelash. The reconstructed cross-sectional image of eyelash was assumed to be an ellipse. The longest diameter of the cross-sectional image was deemed to be the major axis of the fi ber. The minor axis of the fi ber was assumed the longest diameter per- pendicular to the line of major axis. From the length of major axis and minor axis, the area of the fi ber was calculated. The medulla was assumed to be ellipse- and the length of major axis and that of minor axis were measured by the same method of eyelash fi ber measurement. Thickness of cuticle was estimated by defi ning the average of four locations of cuticle space, two of them were contained in the major axis in the fi ber and the other two were contained in the minor axis of the fi ber. Ranking of the degree of crack formation in cuticle. Cracks were observed in the cuticles of eyelashes. The degree of crack formation was ranked into one of fi ve categories: (i) almost Table II Frequency of Eye Makeup Use Frequency Mascara use (n) Eyelash curler use (n) More than 4 times/week 15 16 2 or 3 times/week 3 4 1 time/week 2 3 Almost never 8 4 Never 8 9 Figure 1. Set up of the scanning X-ray microscopy system with an eyelash sample.

JOURNAL OF COSMETIC SCIENCE 220 absent, (ii) one small crack, (iii) several small cracks, (iv) a large crack in a narrow part of the cuticle, and (v) a large crack in a wide part of the cuticle. At fi rst, fi ve typical cross- sectional images agreed with these categories were selected from images of all 36 eyelash samples. Second, other 31 samples were ranked with resemblance to the typical images. Porosity of cortex. The electron density mapping of the reconstructed cross-sectional image of eyelash was binarized. The threshold value of binarized image was determined sensibly to fi t the pore space of each cross-sectional image. The porosity of cortex region was cal- culated using Image J (http://rsbweb.nih.gov/ij/). STATISTICAL ANALYSIS Statistical analyses were performed using SPSS 12.0J for Windows (IBM-SPSS Japan, Tokyo, Japan). The correlations among the categories of age distribution, frequency of mascara and/or eyelash curler, and degree of cracking in cuticle were analyzed by Spear- man’s method using the fi ve ranks of each category. The correlation analyses, thickness of cuticle and porosity of cortex, were performed using Pearson’s method. The correlation analyses between the each category and the each character mentioned above were per- formed using Spearman’s method. RESULTS AND DISCUSSION RECONSTRUCTED CROSS-SECTIONAL IMAGES OF EYELASHES Thirty-six eyelash samples were observed using a differential phase-contrast scanning X-ray microscopic CT system. Typical CT image of an eyelash measured with this system is shown in Figure 2. Three components (cuticle, cortex, and medulla) were observed in the structure of the eyelash. Melanin granules were observed as small white dots in the cortex, indicating that they are relatively dense. Small pores were observed as small black dots in the cortex. These characteristics are very similar to those of scalp hair observed in the previous study Figure 2. Cross-sectional image of an eyelash. The arrow head in the eyelash image indicates a crack in the cuticle.