March 1, 2025
The olfactory environment is an important component of the indoor environment, closely related to health, comfort, and performance. The nervous system, acting as a critical processor for interior and exterior information exchange, regulates the work of other systems. Despite making up just 2 % of all body weight, the human brain uses around 20 % of the circulating oxygen, serving as the primary energy source for maintaining bodily functions and regulating emotions and cognition. Given that aromatic compounds can pass through the blood-brain barrier and engage with receptors in the brain, inhaling aromas has a significant impact on brain function. Electroencephalography (EEG) records the activity of neurons on the covering of the cerebral cortex. Numerous studies have confirmed that EEG usefully reflects how aroma exposure impacts psychophysiological responses.
However, most research has focused on the benefits of EEG in identifying pleasant and unpleasant odors, with fewer studies addressing the stress recovery benefits of plant aromas. Recent clinical studies evaluated the effects of peppermint, rose, and lavender essential oils on stress recovery and brain activity in university students. Brain activity was measured using EEG and stress was assessed by subjective questionnaires. After inhaling the oils, improved mood was reported for each of the oils. Total brain power decreased after inhalation, suggesting a shift towards a more relaxed brain state. Brain oscillatory activity returned to a comfortable state more quickly. The oils also enhanced the brain's self-organized criticality, indicating improved brain resource utilization. Peppermint was particularly effective in improving the brain's order-disorder balance compared to rose and lavender. Rose and lavender showed a more positive impact on brain avalanche activity—a specific pattern of neural activity in the brain that's characterized by bursts of coordinated firing of neurons that spread through the brain like cascading avalanches—in females. Enhanced brain function connectivity—increased clustering coefficient, global and local efficiency, and reducing shortest path length—was also observed, suggesting essential oils improve information exchange in the brain. Overall, the study enhances the understanding of the restorative benefits of plant aromas from the perspective of brain activity, thereby enriching indoor health benefits.