Objectives: Bathing in a bathtub made of hinoki cypress may promote relaxation. This study focuses on changes in autonomic nervous system function, and emotional assessments of individuals who bathed in a hinoki cypress bathtub.

Methods: All 16 study participants bathed twice, as interventions in this study. The baths consisted of bathing in a hinoki cypress bathtub and in a modular bathtub as the control experiment. During the study, participants wore a holter monitor. Before and after bathing, saliva samples were collected for cortisol measurement, and participants underwent a subjective emotional assessment, the Mood Check List-Short Form.2 (MCL-S.2). After bathing, an additional subjective emotional assessment, the Visual Analog Scale (VAS), was performed.

Results and Discussion: The emotional assessments in the MCL-S.2 indicated a significant increase in positive emotional scores (“pleasantness”) after bathing in a hinoki cypress bathtub. The VAS scores showed a significant decrease in the “feeling of fatigue” after bathing in a hinoki cypress bathtub, compared to bathing in a modular bathtub. These results suggest that study participants who bathed in a hinoki cypress bathtub experienced positive effects, and decreased feelings of fatigue. The salivary cortisol concentration decreased significantly after bathing in the hinoki cypress bathtub and in the modular bathtub. For both the hinoki cypress bathtub and the modular bathtub, the high frequency (√HF) values collected with the holter monitor after bathing, were higher than the √HF values collected prior to bathing. The results suggest that bathing in water temperatures of 38-39°C for 15 min enhances relaxation, and has a positive effect on the human body.