EVALUATION OF SKIN COLOR Table IV Summary of Correlation Analysis of u* Versus v* and u* Versus L* and v* Versus L*. r is the Correlation Coefficient, P is the Level of Significance. N.S. Indicates P 0.05 N r•, v, P reL, P rv, L, P Palm: 100 0.28 0.01 -- 0.25 0.05 0.17 N.S. Cheek: 100 0.06 N.S. - 0.41 0.001 0.21 0.05 Arm: 99 0.61 0.001 -- 0.03 N.S. 0.16 N.S. males significant (P 0.05). L* and v* do not differ significantly between male and female. The u* colorindex (redness), the v* colorindex (yellowness) and the L* index of the three skin areas of the subjects are not related to the ages of the persons. For the index u* this is illustrated in Figure 5. The results for v* and L* are similar. The correlation of the chromaticity indices u* versus v* and for u* versus L* for every measured area separately is given in Table IV. The statistically significant correlation (P 0.01) u* versus v* for the arm and the absence of u* versus v* correlation for the cheek can be read from the scatter diagram in Figure 6. The color index relations between the three areas are quantitatively represented in Table V. To discover an overall relationship in the three color indices, measured in the three areas for the sample of 99 subjects a factor analysis was carried out. Every subject of the sample is characterized by nine variables, i.e., 3 (L*, u*, v*) times 3 (palm, cheek, arm). Three factors are orthogonally rotated according to the varimax criterion (14, 15). The loading is a measure of the correlation between the factor and the variable. The results are presented in Table VI. The first factor has positive loadings. Its high loadings are for V1, V2, VS, V7 and VS, or redness index and yellowness index for the palm and the innerforearm and the yellowness index of the cheek. This is a factor of chromaticity. The second factor has positive factors except for redness index of the palm. Its high loadings are for V3 and V9, luminous reflectivity of the palm and the inner forearm. This is a luminous reflectivity factor, excluding the cheek. The third factor is certainly puzzling with only negative and positive loadings. Its high loadings are for V4 and V6. The main emphasis of this factor seems to be on the pigmentation of the facial skin. DISCUSSION The precision of measurement on a particular skin sample tends to be inversely related to its saturation. Psychophysical color difference measurements converted in the L*, u* and v* color space seem to confirm this (16). The color of the skin is determined by the different translucent layers, the particular pigments in each of these layers and the degree of the light scattering due to difference

12 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 25- 20- 15 10, [] [] ß [] [] [] •• [] O[] [] 5 0 lb 2'0 Figure 6. Scatter diagram of u* versus v* for the inner forearm ß and the cheek •n. Only the correlation r•.v. of the inner forearm is significant P 0.001. The regression equation for the forearm is v* = (2.6 + 0.7) + 0.56 u*. in turbidity (3). This translucency of the living human skin and its effects is difficult to investigate at the moment. In maxillofacial prosthetics the main interest is directed towards the facial area. The results in color differences obtained by the colorimetric method between the three investigated areas show a sioe,nificantly higher S.D.,,. and S.D.L. (P 0.01) (Viz. Table III) of the melanin pigmented skin of the cheek than of the relatively unpigmented inner forearm. This relates to the "normal" population variation of pigmented areas. Furthermore, the significantly higher redness u* value (P 0.01) of the cheek and the palm in comparison to the forearm can be explained by the bodily distribution of arterial bloodsupply, sizes of blood vessels and melanine content of the stratum mucosum and the epidermis (3). A similar explanation may hold for the higher v* value of the inner forearm, which may correlate with a higher carotene content. The significantly lower L* of the cheek (P 0.01) an d the palm (P 0.01) compared with the inner forearm is probably caused by the degree of scattering due to a thicker stratum mucosum. The same explanation might hold for the negative relationship