Sleep difficulties are especially common during middle age, including among women in their 40s and 50s. New research suggests that an aromatic oil made from the roots of Hinoki (Chamaecyparis obtusa), also known as Japanese cypress, could offer a simple way to support better sleep at home.

In a study published September 1, 2026, in the Journal of Wood Science, researchers tested Hinoki root essential oil and found several encouraging signs. Participants experienced fewer awakenings during the night, reported feeling better in the morning, and showed brain wave patterns associated with a smoother transition into sleep.

Finding New Value in Hinoki Roots

Hinoki is an important timber tree in Japan, but its roots are often left behind and unused after logging. Those roots contain fragrant compounds that can be extracted to make essential oils.

Scientists have previously investigated oils produced from Hinoki leaves and branches, but oils derived specifically from the roots have received far less attention.

"We wanted to address two questions: whether essential oil production could add value to underused Hinoki roots and whether that oil could improve sleep," says Associate Professor Kuniyoshi Shimizu from Kyushu University's Faculty of Agriculture. "In our earlier work, we examined sleep quality over a single day in a laboratory-like setting. However, sleep is strongly influenced by daily routines and the home environment. Therefore, we decided to examine the effect of repeated use over two weeks in participants' own bedrooms using both subjective assessments and physiological measurements."

Testing Hinoki Oil in Real Bedrooms

The study involved 12 Japanese women between the ages of 35 and 60. Using a single blind crossover design, every participant spent two weeks using Hinoki root essential oil and another two weeks using an unscented control.

Before going to sleep, the women placed three drops of oil into a paper cup and breathed in the scent for 10 seconds. They then positioned the cup about 30 cm from their noses and left it there overnight.

Researchers tracked sleep in several ways. Participants wore a headband that recorded brain waves, used a smartwatch to monitor sleep, and filled out a questionnaire each morning about how they had slept and how they felt upon waking.

Fewer Awakenings and Better Mornings

Repeated exposure to the Hinoki root aroma was associated with improvements across several measures of sleep.

By the 13th day of using the oil, participants said they felt less sleepy after waking and more recovered from fatigue compared with periods when they used the unscented control. Data from their smartwatches also indicated that they woke up fewer times during the night.

The brain wave recordings revealed another potentially important change. After seven days of using the Hinoki oil, participants showed increased delta wave activity around the time they were falling asleep. This pattern is consistent with a smoother progression into deeper stages of sleep.

Participants also responded positively to the scent itself. Compared with the control, they described the Hinoki aroma as more relaxing, comfortable, likable, elegant, nostalgic, and woody.

"By combining physiological measurements with participants' subjective assessments, we were able to examine sleep from multiple perspectives under everyday home conditions, which was an important aspect of this study," emphasizes Shimizu. "Our findings suggest that repeated use of Hinoki root essential oil at home may support sleep initiation, sleep continuity, and feeling refreshed in the morning."

From Forestry Waste to a Potential Sleep Product

The findings could eventually lead to aroma products made from Hinoki roots for bedrooms and other spaces intended for relaxation.

The study also used an unusually simple setup. Participants only needed to place a small amount of essential oil near their beds. That approach could serve as a practical way to study other aromatic materials under normal home conditions rather than relying entirely on laboratory experiments.

There could also be environmental and economic benefits. Turning Hinoki roots into useful aroma products may provide a higher value use for material that is commonly left behind after timber harvesting. The same idea could potentially be applied to other forestry residues that currently go underused.

Because the study was small, more research will be needed to determine which products work best, what doses are appropriate, and how the oil should be used for the most consistent results.