166 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS whole data. Other workers (21,22) have found curvilinear models or linear spline models to be more appropriate for examining age-associated differences in cutaneous aging. However, in this study we employed a linear model for ease of comparison between four anatomical regions. Furthermore, to exclude the defects of the linear model, physical properties at each site were compared between groups with and without wrinkles. The intrinsic tissue characteristic Ue* takes into account the corresponding skin thickness as Ue* = Ue/Ep (Ep, skin thickness in mm). RESULTS RELATIONSHIP BETWEEN VISUAL WRINKLE SCORE AND AGE There was a high degree of correlation between the visual wrinkle score and age for the eye corner of facial skin (Figure 2). Table I shows intercept and slope of primary regression lines between visual wrinkle score and age at several facial skin sites. In a preliminary study, we tried several types of line fitting. From the comparison between age and wrinkle score, the correlation coefficient of the logarithmic model at the eye corner was higher than those of other models. At the other three anatomical regions, the linear model showed the highest correlation coefficients. The degree of wrinkle devel- opment (slope of linear regression line) decreased in the following order: eye corner forehead cheek mouth corner. The age at which the wrinkle score became 3 was calculated from the primary regression line, and was 35.8 in the eye corners, 44.8 in the forehead, 54.2 in the cheeks, and 50.9 in the mouth corners. These results differed slightly from the wrinkle formation rates obtained from the slope. 6 t '--7 z • 11, / me r=0.862 0 [ y :,, • 6.9990, •2 + ,8_q676e,-2x 10 20 30 40 50 60 70 80 Age Figure 2. Correlation between the visual wrinkle score and age ar the eye corner. Using photographs of each subject, wrinkling of several portions of face skin was graded by two trained graders on a five-point scale defined as follows: 1 = none, 2 = mild, 3 = mild/moderate, 4 = moderate, 5 = severe. There was a high degree of correlation between these visual wrinkle scores and age.

FACIAL WRINKLES 167 Table I Intercept and Slope of Linear Regression Line Between Visual Wrinkle Score and Age at Several Facial Skin Sites Linear regression Site Intercept Slope Correlation coefficient Eye corner - 0.069 0.0856 0.862 p 0.001 Forehead - 0.514 0.0784 0.807 p 0.001 Cheek -0.661 0.0675 0.759 p 0.001 Mouth corner - 0.406 0.0668 0.813 p 0.001 RELATIONSHIP BETWEEN PHYSICAL PARAMETERS AND AGE Table II shows the intercept and slope of linear regression lines between physical parameters and age at several facial skin sites. Skin thickness and physical parameters showed a linear increase and a linear decrease with age, respectively. There were different changes in Ur/Uf with age at the eye corner and forehead regions, which are highly susceptible to development of wrinkles. In the forehead, both initial value and the decrease rate were low, while in the eye corners, both initial value and the decrease rate were high. RELATIONSHIP BETWEEN AVERAGE PHYSICAL PARAMETERS AND VISUAL WRINKLE SCORE Calculated on a logarithmic scale (log10/log10), a relationship was observed between average relative parameter Ur/Uf and the degree of wrinkle development (slope of linear regression line between the visual wrinkle score and age) (Figure 3). These findings confirm that the wrinkle formation rate is low, with a high mean Ur/Uf value i.e. wrinkles tend to form in areas with a low Ur/Uf value. There was no such relationship between absolute parameter Ue* and skin thickness. Table II Intercept and Slope of Linear Regression Line Between Skin Physical Parameters and Age on Several Facial Skin Sites Linear regression Parameter Site Intercept Slope Correlation coefficient Thickness Eye corner 1.445 0.00308 0.216 p 0.01 Forehead 1.375 0.00501 0.362 p 0.001 Cheek 1.529 0.00502 0.353 p 0.001 Mouth corner 1.559 0.00174 0. 127 p 0.1 Ur/Uf Eye corner 0.703 - 0.00660 - 0.704 p 0.001 Forehead 0.577 -0.00316 -0.382 p 0.001 Cheek 0.750 -0.00517 -0.643 p 0.001 Mouth corner 0.824 -0.00516 -0.593 p 0.001 Ue* Eye corner 0.335 -0.00314 -0.342 p 0.001 Forehead 0.258 - 0.00129 - 0.160 p 0.05 Cheek 0.298 -0.00184 -0.240 p 0.01 Mouth corner 0.240 -0.00203 -0.316 p 0.001