Exploring the physiological response differences of β-caryophyllene, linalool and citral inhalation and their anxiolytic potential.

Essential oils with β-caryophyllene, citral, and linalool as key compounds often exhibit some anti-anxiety like effects in aromatherapy. However, evidence of the effect of these three compounds through human inhalation remains limited. It is worth exploring their potential anxiolytic effect through the olfactory pathway, and finding out whether the three compounds lead to different physiological responses. A total of 48 subjects were randomly assigned to three odor (β-caryophyllene, citral, and linalool) inhalation groups and one control (odorless jojoba oil) group. Stress stimulation was induced using n-back and mental arithmetic tasks. The odor was administered before the task test session. Assessments including the State-Trait Anxiety Inventory (STAI), electroencephalogram (EEG) activities, facial expressions, several physiological indicators, and a self-report scale of subjective perception of the odor environments were carried out. The changes before and after inhalation, as well as the inter-group differences, were analyzed. Both β-caryophyllene and citral inhalation led to a significant decrease in anxiety levels, while only β-caryophyllene resulted in a notable reduction across both sub-scales of STAI. Following the odor inhalation, heart rate significantly decreased in all three groups, with the β-caryophyllene group exhibiting the most pronounced decline. While the systolic blood pressure of the linalool group demonstrated a statistically significant difference. Regarding facial expressions, β-caryophyllene significantly increased the ratio of 'Happiness' and decreased the ratio of 'Fear'. In the non-task state, citral reduced the power of frontal alpha, delta, and theta waves while β-caryophyllene had a similar effect. All odor inhalation groups showed increased delta and theta waves after the task compared with the control group, with the β-caryophyllene group having notably lower frontal beta waves. β-Caryophyllene and citral exhibited good anti-anxiety effects. Subjects receiving different odors showed different EEG and physiological responses, indicating the differences in emotional regulation ways among the three compounds.