Effect of kabosu (Citrus sphaerocarpa Hort. ex Tanaka) essential oil inhalation on mood, autonomic nervous system activity, and sleep quality in humans

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Background: Kabosu (Citrus sphaerocarpa Hort. ex Tanaka) is a popular Japanese sour citrus fruit that has a distinctive and fresh aroma. This fruit is used not only in traditional Japanese culinary practices but also in the formulation of consumer goods and cosmetic products. Despite these widespread uses, its potential role in aromatherapy remains significantly unexplored. Objective: This study systematically evaluated the psychological and physiological effects of kabosu aroma on mood and autonomic nervous system (ANS) activity, and its potential to improve sleep quality. Methods: In 12 healthy adults, the effects of kabosu aroma inhalation on ANS activity were assessed. For the evaluation of autonomic response, the measurements included pupillary light reflex and fingertip temperature. The effects of kabosu aroma inhalation on mood were evaluated using a visual analog scale. Further, its impact on sleep was examined in a separate group of eight adults who reported experiencing daily fatigue and poor sleep quality. The experimental period of the study was 14 days. Objective sleep parameters were measured using the MicroTag accelerometer. Subjective sleep quality was assessed using the Pittsburgh Sleep Quality Index Japanese version (PSQI-J) and the Oguri–Shirakawa–Azumi Sleep Inventory Middle-Aged and Aged version (OSA-MA). Results: Kabosu aroma inhalation significantly reduced tension and enhanced feelings of clear-headedness and refreshment. Miosis rate and fingertip temperature increased significantly after 2 min of aroma inhalation, indicating kabosu aroma inhalation was associated with changes in ANS responses suggestive of relaxation and may be associated with reduced sympathetic nervous system activity. A subjective evaluation using the OSA-MA showed significant reductions in sleepiness upon waking up and frequent dreaming. Changes in the PSQI-J score were not statistically significant. Objective sleep assessment additionally showed significantly shorter sleep-onset latency, fewer awakenings, reduced get-up latency, and improved sleep efficiency. Novelty of the Study: To our knowledge, this is the first study to systematically examine the effects of kabosu essential oil aroma on mood, ANS activity, and sleep-related outcomes in humans. Conclusion: Kabosu has aromatherapeutic potential and was associated with mood changes and ANS responses suggestive of relaxation. Exploratory findings indicate that sleeping with an ambient kabosu aroma may improve sleep-related parameters and overall sleep quality. Keywords: Kabosu (Citrus sphaerocarpa Hort. ex Tanaka), Japanese citrus essential oil, Aromatherapy, Mood, Autonomic nervous system, Sleep quality