Background: Facial skin care (FSC) is an important routine for Japanese women. Hand motions during FSC physically affect psychological state. However, it is very difficult to evaluate hand motions during personal and complex FSC. The objective of this study was to find out objective and quantitative parameters for hand motions during facial skin care (FSC). Women who enjoy and soothe during FSC (Enjoyment group (E group), n = 20) or not (non-enjoyment group (NE group), n = 19) were recruited by an advance questionnaire. The same lotion, emulsion, and cream were provided to all subjects, and they used sequentially in the same way as the women's daily FSC. The motion of the marker on the back side of the right middle finger during FSC was tracked by a motion capture system. The heart rate variability (HRV) was also measured before and after FSC for evaluating psychological effect.
Results: The averaged acceleration (Avg. ACC), approximate entropy (ApEn), and power law scaling exponent (Rest γ) of the cumulative duration of slow motion from the sequential data of acceleration were evaluated. Compared to the NE group, the E group showed a lower Avg. ACC when using emulsion (p = 0.005) and cream (p = 0.007), a lower ApEn when using emulsion (p = 0.003), and a lower Rest γ (p = 0.024) when using all items, suggesting that compared to the NE group, the E group had more tender and regular motion, and sustainable slow motions, especially in the use of emulsion. In the E group, the low/high-frequency component of HRV decreased significantly after FSC, suggesting suppression of sympathetic activity (p = 0.045). NE group did not. For all subjects, ApEn and Rest γ showed significantly positive correlation with the increase in the low/high-frequency component of HRV after FSC (p < 0.01). ApEn showed significantly negative correlation with the increase in the high-frequency component of HRV after FSC (p < 0.05). Avg. ACC did not show significant correlation with them. These results suggested that the behavior of FSC influences the autonomic nerve system.
Conclusions: ApEn and Rest γ are useful parameters for evaluating quality of hand motions during FSC.
Keywords: Approximate entropy; Autonomic nerve system; Facial skin care; Motion capture; Power law scaling exponent; Relaxation.