Hinoki root oil may reduce nighttime wakefulness

Women exposed to Japanese cypress root volatiles for 13 days reported less morning sleepiness and better fatigue recovery in a small crossover study.

By
Andrea Surnit
October 13, 2026
4 min

MDSpire News

Overview

In a single-blind crossover pilot study of 12 middle-aged Japanese women, nighttime exposure to Kagawa Hinoki root essential oil was associated with less smartwatch-recorded nighttime wakefulness and better self-reported sleepiness on awakening and fatigue recovery than unscented control oil after 13 days. Other measured sleep outcomes, including total sleep duration, sleep efficiency, estimated deep sleep, and overall sleep scores, did not differ significantly between conditions.

Background

Insomnia and disrupted sleep are addressed in current guidance primarily through behavioral treatment: the 2026 American Academy of Sleep Medicine guideline identifies multicomponent cognitive behavioral therapy for insomnia (CBT-I) as foundational for adults with chronic insomnia, and the European Sleep Research Society also recommends CBT-I as first-line. The Hinoki study examined inhaled plant volatiles as a sleep-related exposure, not as an established insomnia treatment. Its findings are from a small home-based pilot in a specific population and were assessed using questionnaires, wearable devices, and electroencephalography rather than polysomnography.

Data Highlights

Study feature or outcome	Reported result
Design and participants	Single-blind crossover study; 12 Japanese women aged 35–60 years who worked daytime shifts. Each completed two 2-week conditions separated by a 1-week washout.
Exposure	Before bed, participants inhaled about 3 drops of Hinoki root essential oil or unscented squalane oil for 10 seconds, then placed the cup about 30 cm from the nose during sleep.
Nighttime wakefulness	After 13 days, smartwatch data from 10 participants showed significantly less nighttime wakefulness with Hinoki oil than control; the condition-by-measurement-period interaction was significant.
Self-reported outcomes	After 13 days, sleepiness upon awakening and fatigue recovery favored Hinoki oil. Sleep maintenance, dreaming, and perceived sleep duration did not differ significantly between conditions.
EEG and other wearable outcomes	After 7 days, the increase in relative delta-wave activity between the first and second 10-minute periods after lying down was greater with Hinoki oil than control. No significant between-condition differences were reported for overall sleep scores, total sleep duration, sleep efficiency, or estimated deep sleep.
Data availability and volatile profile	Sleep scores were available for 8 participants because of recording errors; other smartwatch outcomes were evaluated in 10. Alpha-pinene accounted for 37% of measured volatile peak area, followed by delta-cadinene, gamma-cadinene, limonene, and alpha-muurolene.

Key Findings

The study enrolled 12 Japanese women aged 35–60 years and compared two weeks of nightly Hinoki root oil exposure with two weeks of unscented squalane exposure in a crossover design.
Smartwatch data from 10 participants showed significantly reduced nighttime wakefulness with Hinoki oil after 13 days, with a significant interaction between exposure condition and measurement period.
Participants reported better sleepiness upon awakening and fatigue recovery after 13 days of Hinoki oil exposure; other questionnaire domains—sleep maintenance, dreaming, and perceived sleep duration—did not show significant between-condition differences.
EEG showed a greater increase in relative delta-wave activity between the first and second 10-minute periods after lying down with Hinoki oil than control after 7 days. The authors suggested that Hinoki volatiles may facilitate transition toward deeper sleep.
Overall sleep scores, total sleep duration, sleep efficiency, and estimated deep sleep did not differ significantly between conditions; sleep-score data were available for 8 participants and other smartwatch outcomes for 10.
The study authors noted limitations including small sample size, incomplete physiologic recordings, use of wearable monitoring rather than polysomnography, unmeasured bedroom temperature and humidity, and lack of BMI data; findings were limited to middle-aged Japanese women.

Clinical Implications

The study reports selected sleep-related differences in a small group, while several objective and questionnaire outcomes did not differ significantly between conditions. Current guidance cited in the supplied context identifies CBT-I as first-line or foundational care for chronic insomnia; the Hinoki pilot does not establish aromatherapy as a standard treatment.

Conclusion

Nighttime Hinoki root oil exposure was associated with reduced wearable-recorded wakefulness and improvements in two self-reported outcomes in this pilot study. The limited sample and mixed outcome results constrain interpretation and generalizability.