Shichun Pei’s research while affiliated with Shanghai Jiao Tong University and other places

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.

Olfactory perception, and especially affective responses of odors, is highly flexible, but some mechanisms involved in this flexibility remain to be elucidated. This study investigated the odor perceptions of several essential oils used in aromatherapy with emotion regulation functions among college students. The influences of people’s characteristics including gender, hometown region, and fragrance usage habit on odor perception were further discussed. Odor perception of nine essential oils, which can be divided into the ester-alcohol type (e.g., lavender oil) and terpene type (e.g., lemon oil) were evaluated under three odor concentrations. The results indicated that chemical type, but not concentration, significantly influenced the odor perception and there was no interaction between the two factors in this study. The arousal and emotional perception scores of odors with terpene-type oil were significantly higher than odors with ester-alcohol type. In terms of people’s characteristics, participants from the southern Yangtze river gave a higher familiarity rating to almost all of these odors. The habits of fragrance usage also significantly influenced some of the odors’ subjective intensity and emotional perception ratings. However, there were no significant gender differences in most of the odor perceptions. In addition, familiarity and pleasantness were positively correlated, and emotional perception and subjective intensity also showed a weak correlation. These results suggested that users’ cultural characteristics could be considered to be important factors that affect the essential oil’s odor perception in aromatherapy.