EEG changes associated with stress reduction in university students following exposure to essential oil odors

Stress among university students has become a significant public health concern, prompting growing interest in non-pharmacological interventions. Essential oil inhalation has been suggested as a potential approach to stress reduction; however, quantitative comparisons of electroencephalographic (EEG) responses to commonly used essential oils remain limited. This study investigated EEG changes following inhalation of six essential oils (lemon, rosemary, tea tree, lavender, eucalyptus, and chamomile) in 33 university students between February and June 2025. EEG signals were recorded using an 8-channel system covering the prefrontal, frontal, temporal, and parietal regions. Relative EEG power values, derived indices (RAB, RAHB, and RST), regional alpha activity, and inter-electrode connectivity were analyzed. The study employed a within-subject pre-post design without a separate control group. Pre- and post-inhalation changes were evaluated using paired-sample t-tests, and differences among oils were further examined using repeated-measures MANOVA. Across all essential oils, relative alpha power increased, while beta power generally decreased. Significant increases in RAB were observed for lavender, tea tree, chamomile, and rosemary, whereas RAHB increased significantly for lavender, rosemary, eucalyptus, chamomile, and tea tree. RST showed slight increases across all oils, but none reached statistical significance. The overall multivariate effect of odor on changes in RAB, RAHB, and RST was not statistically significant, although RAHB showed a significant difference among oils in the exploratory follow-up analysis. Relative alpha activity was highest in the parietal region. Connectivity among the prefrontal, frontal, and temporal regions generally increased following essential oil inhalation, whereas connectivity between these regions and the parietal region tended to decrease. Connectivity within the left hemisphere decreased slightly, while connectivity within the right hemisphere and between hemispheres increased, suggesting a redistribution of connectivity patterns. Descriptive patterns also indicated a tendency toward increased connectivity for lemon, rosemary, and tea tree and decreased connectivity for lavender, eucalyptus, and chamomile. These findings provide preliminary quantitative neurophysiological evidence of EEG changes associated with essential oil inhalation and may inform the potential application of olfactory stimuli in restorative indoor and outdoor campus environments.