Sensibility Evaluation of an Exfoliating Lotion with Supreme Tactile Impression during Wiping Motions

Abstract

We aim to provide cosmetics that appeal to users’ “sensibility” and have accordingly developed cosmetics based on a sensibility evaluation. We examined exfoliating lotions that can be applied to a cotton pad and gently wiped across the stratum corneum, i.e., the outermost layer of the skin. Our method correlates the visualized psychological structure with measured physical quantities. To visualize the psychological structure when using an exfoliating lotion, we selected appropriate evaluation words and conducted a one-month usage test. Using factor analysis, we evaluated nine factors that are related to the value judgments of subjects using the exfoliating lotions. Next, we analyzed the causal relationships between these factors via structural equation modeling and modeled the psychological structures of the users. The model fit indices were satisfactory (GFI = 0.952; RMSEA = 0.000). The subconsciously important perceptions appeared to be “frictional feeling” and “wiped-off feeling,” both of which are derived from the tactile impression imposed by the wiping motion. Next, we analyzed the relationship between the frictional force and the tactile impression. To evaluate the physical quantities related to the “frictional feeling” and the “wiped-off feeling,” we examined the frictional force of wiping. For 12 types of exfoliating lotions, we measured the dynamic friction coefficient and the time profile of the frictional force. The dynamic friction coefficient was measured using a friction tester while mechanically wiping the artificial skin. The time profile was measured using an in-house designed dedicated device while subjects wiped the lotions from the artificial skin. The factor scores calculated from the subjective evaluation were then correlated with the dynamic friction coefficients. The “frictional feeling” and “wiped-off feeling” showed inverse correlations with the dynamic friction coefficient, and we found that they could not be evaluated as independent elements (with correlation coefficients of r = −0.820 and 0.744, respectively). Therefore, to identify physical quantities that can independently affect the two factors, we extracted the eight-dimensional vibrational feature quantities in the time–frequency domain from the time profile and correlated them with the factor scores in a multiple regression analysis. The factor scores of the “frictional feeling” and the “wiped-off feeling” were estimated with high accuracy (r = 0.672 and 0.722, respectively). Each factor corresponded to a different vibrational feature, confirming that the factors are physically independent. This result suggests that both factors can be simultaneously increased by controlling the frictional force. Based on this result, we attempted to develop an exfoliating lotion that enhances the vibration features and consequently intensifies the two examined factors.