A scent that was noticeable when you entered a room may fade from your attention after a while. Have you experienced this when using a diffuser? You may feel like adding more fragrance, but looking at the intervals between releases, not just the amount, can offer a different perspective.
In August 2024, Narae Choi and colleagues at Toyo University published an experiment involving intermittent diffusion of sweet orange essential oil. They examined how people perceived the scent, whether it was acceptable as a fragrance in a learning space, and whether task performance differed.
Five Minutes or Ten: What Did the Experiment Change?
The participants were 21 healthy university students aged 18–28. They entered a small experimental space at Osaka University one at a time and evaluated the scent under different settings of a nebulizing diffuser that dispersed essential oil as a fine mist.
There were four conditions: a 5-second release on a 5-minute cycle; a 7-second release on a 10-minute cycle; a 10-second release on a 10-minute cycle; and a comparison condition using brief releases on approximately 1-minute cycles to keep the scent concentration relatively constant. A “10-minute interval” did not mean spraying continuously for 10 minutes. Only the initial release was longer, to raise the concentration more quickly.
The two 10-minute-cycle conditions were not simply comparisons with longer pauses. The 7-second release was intended to match the peak concentration of the 5-minute-cycle condition, whereas the 10-second release was intended to match its average concentration. The concentrations here were calculated from factors such as the amount released and the ventilation rate. They were not actual measurements of essential-oil compounds in the air.
Changes in Scent Do Not Reach Everyone in the Same Way
In the first experiment, participants rated scent intensity, preference, and other attributes every 30 seconds for 32 minutes under each condition. On average, the spaced-release conditions produced a pattern of stronger perception after release and weaker perception before the next one. Under the relatively constant-concentration condition, perceived intensity fell over approximately the first 5 minutes and then stabilized.
Individual responses varied, however. Some people perceived changes in intensity aligned with the release cycle, others perceived little change, and still others reported changes unrelated to the cycle. Some who found it difficult to detect changes on the 5-minute cycle appeared better able to do so on the 10-minute cycle.
Preference tended to decline with repeated releases on the 5-minute cycle. Neither of the two 10-minute cycles showed that tendency. Reintroducing a scent frequently does not necessarily keep it feeling pleasant.
“I Would Like to Study Here” Is Not the Same as “My Scores Improve”
Participants were also asked to imagine studying amid the scent in a lecture room, a self-study room, or at home, and to rate its acceptability. For the imagined self-study room, the 10-second release on a 10-minute cycle and the approximately 1-minute comparison condition were rated more highly than the 5-minute cycle, with statistically significant differences. This was not a result from actual classrooms, nor did it show that a 10-minute cycle was superior in every setting.
In the next experiment, the same 21 participants experienced both an unscented condition and the 10-second release on a 10-minute cycle on separate days. They spent 20 minutes each on an attention task searching for specified characters among other characters, proofreading, and questions on classical Japanese.
The scented environment was rated higher than the unscented one for preference and pleasantness. However, there were no significant differences in feeling concentrated, sleepiness, fatigue, motivation, or similar measures; nor were there significant differences in the scored attention and proofreading tasks when averaged across all participants. The classical Japanese questions were not scored.
Liking the scent and performing better on a task need to be understood separately. This experiment does not allow us to say that releasing orange scent every 10 minutes improves concentration. Equally, because the sample was limited, it does not establish that there is no effect under every possible condition.
Can the Settings Be Transferred Directly to a Home Diffuser?
The experimental space was approximately 3 m long, 1.3 m wide, and 2 m high. Air passed through activated-carbon filters was supplied at 90 cubic meters per hour, and two fans distributed the scent. If room size, ventilation, or the diffuser’s output differs, the way scent lingers will change even with the same timing settings.
Only one scent was used: sweet orange essential oil. It is not known whether the same interval would suit other essential oils, perfumes, or reed diffusers. This study did not establish an optimal home timer setting or a safe amount to use.
One takeaway for daily life is that increasing the amount is not the only way to think about a scent that seems weaker. Within the limits of the device’s instructions, consider whether it needs to run continuously. Even if the scent seems subtle to you, check how others in the same room feel about it. These are not research-validated procedures, but practical ways to explore everyday comfort.
Summary
When enjoying a room fragrance, continuously perceiving it clearly need not be the only goal. In this study, the interval between releases affected how changes were perceived and how much the scent was liked. At the same time, perceptions varied between individuals, and greater comfort did not translate directly into better task performance.
The authors aimed to create an environment that maintained comfort while avoiding unnecessary fragrance exposure. The fact that many participants still perceived the scent before the next release offers a clue for considering intervals and amounts while distinguishing maintained perception from continuously emitting fragrance. However, this was not a study that established safety by measuring airborne compound levels or health effects.
References
Authors: Narae Choi, Toshio Yamanaka, Akihisa Takemura, Tomohiro Kobayashi, Masato Hirano
Article title: Intermittent essential oil diffusion in learning spaces: Exploring olfactory responses and cognitive effects
Journal: Building and Environment, 264 (2024), 111918
Online publication date: August 6, 2024
DOI: 10.1016/j.buildenv.2024.111918
Original study: Publisher’s article page
Research funding: Daikin Industries. The authors disclose financial support from the company in the declaration of competing interests.
Original study license: CC BY-NC-ND 4.0. This article is an independently written explanation based on the research facts, not a republished translation of the paper. No figures or tables from the original study have been used.
