Before bed, each of 12 Japanese women put three drops of hinoki root oil on a paper cup, breathed in for 10 seconds and set the cup about 30 centimeters from her nose for the night. Over two weeks of that routine, smartwatch data showed fewer nighttime awakenings than during two weeks with an unscented oil. Kuniyoshi Shimizu, an associate professor in Kyushu University’s Faculty of Agriculture, led the pilot.
Kagawa hinoki root oil and the bedside paper cup
Hinoki is the Japanese cypress, Chamaecyparis obtusa. The oil in the trial came from roots of trees grown in Kagawa Prefecture, material that is often left unused after logging. Shimizu’s team wanted to test whether the oil could add value to forestry leftovers, and whether it did anything for sleep at home. His earlier work, he said, examined sleep over a single day in a laboratory-like setting, whereas “sleep is strongly influenced by daily routines and the home environment.” The paper lists the most abundant volatile compounds in the oil as alpha-pinene, delta-cadinene, gamma-cadinene, limonene and alpha-muurolene.
The study, titled “Sleep improvement by Kagawa Hinoki root volatiles in middle-aged women: a home-based pilot study,” ran in participants’ own bedrooms. Twelve women aged 35 to 60 took part, with a mean age of 46, in a single-blind crossover: two weeks with the root oil and two weeks with squalane oil as the no-scent control. Squalane is odorless, so the comparison was scent against no scent. Each woman served as her own comparison. The paper appeared on Sept. 1, 2026 in the Journal of Wood Science.
Smartwatch awakenings, brain waves and morning reports
Three kinds of data were gathered over each two-week block: a wearable headband that recorded brain activity, a smartwatch that tracked sleep, and a morning questionnaire. According to the paper, the smartwatch detected fewer awakenings after 13 days of use. Kyushu University’s release on the study says the same, and neither document publishes the actual awakening counts or a p-value, so the size of the drop is not available to readers. The awakenings figure also comes from a wearable device at home, not from a sleep-clinic recording, which makes it a convenient but looser measure of how often a sleeper actually surfaced.
The other results are modest in kind. By day 13 the women reported, on the OSA sleep inventory questionnaire, feeling less sleepy on waking and more recovered from fatigue than with the control, the two factors where the root oil stood out. Brain recordings showed more slow-wave activity from day 7, which the Kyushu team links to a smoother passage into deeper sleep. The women also rated the root oil’s smell as more relaxing, comfortable, likable, elegant, nostalgic and woody than the control.
Shimizu said that “repeated use of Hinoki root essential oil at home may support sleep initiation, sleep continuity,” the phrasing of a researcher describing a possibility, not a treatment. He also said the home setting let the team “examine sleep from multiple perspectives under everyday home conditions,” which is the design’s main advantage over a one-night lab test: the women slept in their own beds, on their own routines, for a fortnight at a stretch.
A dozen participants, one supplier and an open evidence base
Twelve women, one scent and a single-blind design (the participants did not know which oil they had, though the people running the trial did) is a pilot by any measure. The oil was supplied by Ouken Co., Ltd. The paper states that the company had no control over the design, analysis, interpretation or writing, though three authors are affiliated with it, and that the authors declare no competing financial interests. Funding came from Kyushu University and the collaboration with Ouken.
The pages read for this article also leave out the inclusion criteria, any ethics-approval details and a dedicated limitations section. What they do say plainly is that the best products, doses and usage conditions are undetermined, and the proposed uses, aroma products for bedrooms and relaxation settings and a simple home-use method for testing other aromatic materials, are suggestions from the authors, not outcomes of the trial.
The authors say further work is needed to determine appropriate products, doses and usage conditions. Scent-and-sleep work in general has the same small-sample footing: a 2021 Scientific Reports pilot of lavender oil during sleep used nine young adults and also reported a rise in slow-wave sleep. The U.S. National Center for Complementary and Integrative Health says little rigorous research has been done on aromatherapy for insomnia, and that it is not known whether it helps.
The ScienceDaily write-up of the Kyushu release that circulated on Oct. 6 adds no new data. The hinoki result rests on 12 women and two weeks of watch readings, with no counts released to check them against.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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