88 JOURNAL OF COSMETIC SCIENCE SALIVARY CORTISOL The salivary cortisol levels before and after the face-washing procedure using each of the three samples are shown in Table III. There were no significant differences in cortisol levels between the three samples in either the pre- or post-procedure measurements. The magnitudes of the cortisol changes for all samples are shown in Table IV. Cortisol levels changed significantly more in response to sample C than sample A (p 0.05), while the response to sample B was not significantly different from the other two (p 0.05). DISCUSSION In this study, we assessed the effect of face-washing on the emotional response of participants using three types of foam with different viscosity levels. For all foam samples, the OFC (BA11), which plays a role in rewarding behaviors, was stimulated in response to experiencing the samples on both the hands (phase 1) and face (phase 2). The neural activities of the OFC (BA11)16,17 and ACC (BA32),18,19 which are involved in motivation and cognitive judgment/decision-making based on rewarding emotions, respectively, were significantly higher than those elsewhere in the brain. Given that tactile stimuli can cause changes in cognitive processes and emotions,8 our results suggest that foam-mediated tactile stimulation may cause an emotional response. We found that in response to samples A and B, the participants’ neural activity was relatively higher in the left cerebral hemisphere than in the right one. In contrast, the signal was higher for the right frontal lobe than for the left frontal lobe in response to sample C in both phases. In a previous study, EEG responses observed during pleasant emotions Table III Comparison of Salivary Cortisol Pre-test Post-test p-value Sample A Sample B Sample C Sample A Sample B Sample C Phase Foam Interaction Salivary cortisol (nM) 6.7 ± 4.5 7.1 ± 3.9 5.0 ± 2.3 5.4 ± 2.5 6.2 ± 3.5 7.8 ± 3.9 0.88 0.89 0.21 Notes: Values are presented as means ± standard deviations. Pre-test: before a series of facial cleansing procedures post-test: after a series of facial cleansing procedures. Sample A: foam with low viscosity sample B: foam with medium viscosity sample C: foam with high viscosity. A two-way ANOVA with a Bonferroni post hoc analysis was performed for statistical evaluation. Table IV Comparison of Changes in Salivary Cortisol Sample A Sample B Sample C p-value Magnitude of salivary cortisol change (nM) −1.35 ± 3.3 (−6.7 to 2.3) −0.9 ± 3.6 (−4.8 to 5.7) 2.7 ± 2.4 (−0.5 to 6.5)† 0.03 Notes: Values are presented as means ± standard deviations (minimum value−maximum value). Sample A: foam with low viscosity sample B: foam with medium viscosity sample C: foam with high viscosity. Magnitude of change =post-test value minus pre-test value. †Sample A versus sample C p 0.05.

89 Tactile Stimulation Effects on EEG Signals were higher in the left hemisphere, whereas during unpleasant emotions, they were higher in the right hemisphere.20 Therefore, we inferred that the tactile stimulation elicited by samples A and B induced more pleasant feelings in the participants, while sample C evoked more unpleasant feelings. Similarly, the salivary cortisol tended to increase from the baseline in response to sample C, while it slightly decreased after using samples A and B, although the changes with each sample before and after treatment were not significant. It has been reported that salivary cortisol levels decrease during relaxation21,22 and increase under stressful conditions23,24 therefore, we inferred that the tactile stimulation and facial cleansing experience with sample C (with high viscosity) were more stressful than those with samples A and B. Conversely, samples A and B (with low and moderate viscosity, respectively) seemed to evoke more pleasant feelings. Previous studies reported that pleasant tactile stimuli cause a significant increase in neural activity in the OFC (9) and ACC.25 The EEG measurements in the current study demonstrated that the neural activity in BA11 and BA32 was significantly higher in both phases using samples A and B than with sample C. Therefore, we conclude that the tactile stimuli of samples A and B evoked more pleasant emotions than those of sample C. We further found that upon stimulation with sample A, the recorded neural activity in both BA11 and BA32 was significantly higher in phase 2 than in phase 1. This suggests that participants’ emotions changed between perceiving the foam on their hands and perceiving the foam on faces. BA11 responds to sensory input and generates value representations by encoding combinations of stimuli, leading to motivated behavior.16 In addition, BA32 (the ACC region) is also involved in generating value representations, and its emotional processing function is generally considered to induce motivation. The ACC plays an important role in inferring and judging current and future situations based on extrinsic experiences from the external environment, leading to appropriate behavior.26 This information may help us understand the effects observed upon foam application to the face. During the foam application to the cheeks in phase 2, before spreading it upon the whole face, neural activity in these brain regions may have been stimulated by enhanced motivation toward the act of washing the face, based on the positive experience of tactile stimulation in phase 1. However, the reason this tendency was observed only with sample A remains unclear. This study has several limitations: first, the number of participants was small (n =12), and only females were included. Future studies should enroll a greater number of participants, including males. Second, in addition to its viscosity, other properties of the foam were not considered. Thus, subsequent studies should investigate the effects of other relevant characteristics on participants’ emotions, such as foam density and shape retention. Third, we only examined some aspects of face-washing. In the future, it will be necessary to examine changes in neurophysiological indices throughout the whole face- washing procedure. Despite these limitations, our results indicate that the potential emotional changes evoked by different tactile stimulation according to foam viscosity can be captured via neurophysiological indices, and that these emotions can change during specific segments of the face-washing procedure. We believe that our findings will provide valuable information for developers of facial cleansers and hand soaps. They will also be useful for investigating other foam characteristics and in designing research to develop products that improve the users’ physical and emotional experience.