Physiological and Psychological Effects of Scent of Soil on Human Beings

Abstract

This study examines heart rate and heart rate fluctuation when subjects are presented with the scent of soil and their psychological changes as expressed by scores of the Profile of Mood States (POMS) and Visual Analog Scale (VAS) as indexes. In the experiment, we directed the subjects to rest in a sitting position for 5 min. (Pre.), to smell the scent for 1 min. (No Stim., Stim.), and to rest in a sitting position for 15 min. (Post 5, Post 10, Post 15). Psychological evaluation was performed before and after the experiment (Pre., Post). The scent stimulation was made by opening/closing a bottle with screw-on cap that contained the soil. In the control group, the bottle is always closed. In the stimulus group, the bottle was opened only at the time of Stim. For the physiological evaluation, although we could observe no change in the control group, in the stimulation group, the subjects’ heart rates decreased at Stim. and Post 15. For the psychological evaluation, VAS scores of “Feel relaxed” and “Feel soothed” increased and POMS scores of “Strain-Uneasiness”, “Anger-Hostility”, and “Confusion” decreased. In open-ended questions, some of the subjects recalled memories of insect-collecting, horticulture, forests and parks. There was a negative correlation between heart rate decrease (Stim.) and increase in the VAS scores of “Feel relaxed” (r = -0.896, p < 0.001) and “Feel soothed” (r = -0.684, p = 0.014). The healing effects from the scent of soil included subjects’ memories that were considered to have influenced the heart rate.