Do Pleasant Wood-Scented Rooms Produce Matching Bodily Responses?

Rooms with more hiba wood were perceived as more natural and traditional, and their scent was rated more pleasant. Physiological responses, however, did not change uniformly to a greater extent as the amount of wood increased. A 2011 study compared subjective impressions and bodily responses to different uses of wood in four full-size rooms.

The results make an important distinction: finding a wood scent pleasant and observing changes in blood pressure or salivary markers are questions that need to be examined separately.

Hiba flooring, wainscoting, or full walls

The participants were 14 healthy university students living in Aomori Prefecture, seven men and seven women. On the same day, each experienced the following four rooms, which differed in their use of hiba wood.

• Standard room: No hiba wood. Other wood was used for the floor and some other elements.
• Room 1: Hiba wood mainly on the floor, covering 20.6% of the interior surface area.
• Room 2: Hiba wood on the floor, wainscoting, and other elements, covering 42.8%.
• Room 3: Hiba wood on the floor, walls, and other elements, covering 68.0%.

Room dimensions, lighting, temperature, humidity, and other conditions were matched, and the order of entry was adjusted for each participant. In each room, participants first rested with an activated-carbon mask on and their eyes closed to limit stimulation. They then removed the mask and opened their eyes. The appearance and scent of the wood were presented together, while pulse rate and blood pressure were measured for 180 seconds.

Mood and fatigue were assessed before and after exposure, and salivary alpha-amylase activity was also measured. Participants rested for about 60 minutes between rooms. The analyses of room-image ratings and salivary alpha-amylase included 12 participants, excluding two with missing measurements.

More hiba wood meant a stronger perceived scent

After all experiments were complete, the rooms were ventilated and conditioned as in the experiment, and their air was analyzed. Sesquiterpenes such as thujopsene and cedrol, thought to originate from hiba wood, were detected. Their airborne concentrations increased with the amount of hiba wood used.

These compounds were also detected in the standard room. That room had no hiba wood in its interior, but it was not an environment entirely free of wood or aroma compounds. The concentrations were also not measured continuously during each participant’s exposure: they were measured afterward under matched conditions.

Participants likewise tended to perceive a stronger odor in rooms with more hiba. Room 3 was rated significantly stronger than the other three rooms, and Room 2 significantly stronger than the standard room. Odor ratings were on the pleasant side in every room, and Room 3 was perceived as significantly more pleasant than the standard room.

Hiba floors and walls changed impressions of naturalness and fatigue

Compared with the standard room, Room 3 received significantly higher ratings for naturalness and a traditional feel. On the POMS mood questionnaire, the change in the fatigue score was lower in Room 3 than in the standard room, indicating a greater reduction in perceived fatigue after the brief exposure.

Not every psychological measure changed in the same way, however. There were no significant differences between rooms in feelings of calmness, liking or goodness ratings for the room, or POMS vigor. An overall between-room test found a difference in general pleasantness, but subsequent pairwise comparisons did not establish significant differences.

The findings therefore primarily concerned the natural and traditional impression, pleasant scent, and change in fatigue associated with the room that used hiba on both its floor and walls.

Bodily markers also changed in the room with mainly hiba flooring

Salivary alpha-amylase is one marker associated with autonomic nervous activity and other processes. It increased by an average of 7.1% after exposure in the standard room, whereas it decreased by 45.6% in Room 1, where hiba was used mainly on the floor, and by 41.1% in Room 2, which had hiba flooring and wainscoting. In the pairwise comparisons, the significant finding was a lower rate of change in Room 1 than in the standard room.

Blood pressure showed further differences over time. Systolic blood pressure temporarily fell relative to the prestimulus level in the three rooms containing hiba. Significant reductions were reported at 30–70 seconds in Room 1, 30–90 seconds in Room 2, and 30–50 seconds in Room 3. From 100 seconds onward, however, no room showed a significant change.

Diastolic blood pressure fell during some time intervals in all four rooms, including the standard room. Pulse rate showed no significant overall change under the study’s decision rule.

The significant blood-pressure differences here were comparisons between the periods immediately before and after stimulation within each room. A longer period of significance in one room does not directly establish that it was better than the others. Blood pressure was compared repeatedly at 10-second intervals, and the researchers also used their own rule: an overall change was recognized when at least three of the 18 intervals were significant.

Pleasant impressions and physiological responses did not follow the same ranking

In the psychological assessments, Room 3, which contained the most hiba, stood out for naturalness and the change in fatigue. The difference from the standard room in salivary alpha-amylase, however, was established in Room 1, which contained less hiba. This is the basis of the authors’ central conclusion that psychological evaluations and physiological responses did not correspond.

The authors suggested possible explanations involving the combination of appearance and scent, and the visual stimulation associated with extensive use of wood. Because participants opened their eyes and began smelling the room at the same time, however, the contributions of these two factors could not be separated.

The findings also concern 14 people exposed for only a few minutes. The study is best read as an experiment examining impressions of a space and short-term bodily responses through several measures, rather than as evidence establishing long-term recovery from fatigue, health benefits, or an optimal proportion of wood in a home.

Summary

The room with hiba flooring and walls was perceived as more pleasantly scented, natural, and traditional than the standard room without hiba, and its fatigue scores decreased more. In contrast, the room with hiba mainly on the floor was the one in which the rate of change in salivary alpha-amylase was significantly lower than in the standard room. Blood-pressure changes were also short-lived and did not follow a uniform pattern according to the amount of wood.

When considering a comfortable room, odor intensity and subjective impressions alone cannot establish its effects on the body. Examining the effects of seeing and smelling wood separately is a next step toward understanding these findings.

One author listed Sugiyama Mokuzai Co., Ltd. as an affiliation at publication. No separate funding or conflict-of-interest declaration section was identified.

References

Kimura, A., Sugiyama, H., Sasaki, S., & Yatagai, M. (2011). Psychological and Physiological Effects in Humans Induced by the Visual and Olfactory Stimulations of an Interior Environment Made of Hiba (Thujopsis dolabrata) Wood. Mokuzai Gakkaishi, 57(3), 150–159. doi:10.2488/jwrs.57.150 (Full original article)