Numerous studies have reported a significant increase in stress experienced by students owing to the COVID-19 pandemic. Recently, interest in stress management using nature-derived substances has increased. However, studies examining the effects of olfactory stimulation by fir are lacking. The aim of this study was to investigate the physiological and psychological effects of inhaling fir essential oil. Additionally, differences between male and female participants were compared. Twenty-six university students (16 female and 10 male students; mean age, 21.5 ± 1.9 years) participated in this study. Fir essential oil was used for olfactory stimulation, with normal room air as the control. The odor was administered for 3 min. Heart rate variability and heart rate were used as indicators of autonomic nervous system activity. The Profile of Mood States and State-Trait Anxiety Inventory were used as psychological indicators. The ln(Low Frequency/High Frequency) ratio, which is an indicator of sympathetic nervous activity reflecting a stressful or aroused state during stimulation with fir essential oil, was significantly lower than during the control condition. Assessment of psychological indicators showed that the positive mood of "vigor" improved significantly and negative moods of "tension-anxiety", "depression", "anger-hostility", "fatigue" and anxiety levels reduced significantly after inhaling fir essential oil compared to the control condition. This study showed that inhalation of fir essential oil has physiologically and psychologically relaxing effects, with differences in results depending on the sex of the participants.
Keywords: fir essential oil; forest healing; forest therapy; heart rate; heart rate variability; profile of mood states; relaxation; sex comparison; state-trait anxiety inventory; stress relief.