Three drops on a paper cup, ten seconds of breathing in, then the cup stays about thirty centimetres from the nose all night. That, according to the Kyushu University press release, is how twelve Japanese women used essential oil from the root of hinoki, the Japanese cypress Chamaecyparis obtusa, for two weeks.
The study appeared in the Journal of Wood Science on 1 September 2026, as an accepted manuscript rather than the final version. The first author is Fadilla Zennifa and the corresponding author is Kuniyoshi Shimizu, of Kyushu’s Faculty of Agriculture. The manuscript reached the journal on 5 August 2025 and was accepted on 21 July 2026, almost a year later. ScienceDaily ran it on 6 October.
The participants were aged 35 to 60, 46 on average, and slept poorly. The design is a crossover. Each woman used the hinoki oil for two weeks and an odourless control, squalane oil, for another two, so each served as her own comparison. The trial was single-blind, meaning participants were not supposed to know which oil they had. The part of the article available to us does not give the order of the two phases, any randomisation, the gap between phases or the entry criteria.

Sleep was measured four ways. A Japanese questionnaire, the OSA sleep inventory MA version, rates how one feels on waking. An electroencephalogram records slow waves, the mark of deep sleep. A smartwatch counts night-time awakenings. A visual scale collects the women’s ratings of the scent and their mood.
According to the authors, with hinoki oil slow-wave activity rises from day seven. After day thirteen, sleepiness on waking and recovery from fatigue improve, two of the questionnaire’s factors, and the smartwatch records fewer awakenings. The women rated the scent as more relaxing, comfortable, elegant and nostalgic than the control, and also stronger and more bitter. The most abundant compounds in the oil are alpha-pinene, delta-cadinene, gamma-cadinene, limonene and alpha-muurolene.

The text available to us gives no numerical values, statistical tests or confidence intervals. With twelve people the uncertainty around every measure is wide, and the authors themselves call the work a pilot.
The oil was supplied by Ouken, a company in Takamatsu, in the Kagawa prefecture that gives the product its name. Three of the eight authors are affiliated with Ouken. The work was supported by Kyushu University and by a collaboration with the same company. The authors state that Ouken had no role in design, analysis, interpretation or writing, and declare no competing financial interests. The statement sits next to three company bylines.
How blind the trial really was remains open. The control had no smell, and participants rated the hinoki oil as stronger in scent. A woman who notices a distinct fragrance knows she is not holding the control. Subjective measures, the questionnaire and the visual scales, are the most exposed to this. The smartwatch and the electroencephalogram are less so.
ScienceDaily’s headline promises sounder sleep from a few drops. The paper reports that in twelve women, over two weeks, some sleep measures moved in the hoped-for direction. Going further would need more participants, declared randomisation, the actual numbers and a control that also has a scent.

References
Zennifa F., Isa A., Tomimatsu E., Xu Y., Taki R., Yasutomi H., Yasumori N., Shimizu K., "Sleep improvement by Kagawa Hinoki root volatiles in middle-aged women: a home-based pilot study", Journal of Wood Science, 2026, accepted manuscript published online 1 September 2026, open access. doi: 10.1186/s10086-026-02296-3
Kyushu University, press release via ScienceDaily, "A Few Drops of This Japanese Tree Oil May Help You Sleep More Soundly", 6 October 2026.