The feeling that an appetizing smell makes your mouth water is familiar. But what happens when room brightness and warming the feet are also considered? In an experiment with 10 healthy men, the amount of saliva increased from before to after smelling pineapple under relatively low illuminance.
This 2021 study examined saliva secretion in relation to three features of the living environment: illuminance, fragrance, and a footbath. Rather than measuring fragrance in isolation, it considered the surrounding conditions as well.
Four conditions under two levels of brightness
The participants were 10 nonsmoking men aged 20–30, with no history of diseases that reduce saliva secretion. Each experienced low illuminance of 228 lx and high illuminance of 2039 lx on separate days. On each day, four conditions were conducted in random order: no stimulation, fragrance alone, a footbath alone, and fragrance with a footbath.
Each condition lasted 60 minutes: 10 minutes of rest, 10 minutes of fragrance or footbath stimulation, and another 40 minutes of rest. Participants worked on an undemanding jigsaw puzzle, with breaks, to avoid falling asleep. Sessions were held at comparable times of day, with restrictions on food, caffeine, and alcohol and exercise on the preceding day.
A commercial pineapple fragrance was applied to a smelling strip and presented approximately 3 cm from the nose. The footbath lasted 10 minutes at 40°C. Five fragrances had been compared beforehand, and pineapple was selected because it produced the largest increase in saliva in that preliminary assessment. The original paper calls it an “essential oil,” but provides no details of its composition or production method.
An increase in the low-light, fragrance-only condition
Saliva was collected in a container every five minutes and weighed. Statistical comparisons used the 10-minute periods before stimulation, during stimulation, and at the end of the experiment. The “after stimulation” measurement was therefore not immediate: it covered 30–40 minutes after the fragrance or footbath ended.
With fragrance alone under low illuminance, the mean amount of saliva over 10 minutes increased significantly from 3.03 g before stimulation to 4.21 g afterward. The mean during stimulation was 4.51 g, but its comparison with the prestimulation value was not significant. A larger average and a statistically established change that accounts for differences between people are not the same thing.
In the high-illuminance fragrance condition, the mean was 3.01 g before and 3.56 g after stimulation, with no significant change. Neither the footbath-only condition nor the combined fragrance-and-footbath condition showed significant changes over time at either illuminance. The no-stimulation condition also showed no significant change over time.
This comparison does not establish that darker is better
The important point is that the original paper mainly compared the before, during, and after periods within each condition. It did not report tests directly comparing the amount of change with versus without fragrance, or under low versus high illuminance.
A significant increase only in the low-illuminance fragrance condition offers a lead for future research. On its own, however, it does not establish that fragrance is superior to no fragrance, or that dimming the lights strengthens its effect. Nor does the absence of a significant change in the combined condition prove that a footbath cancels out the effect of fragrance.
The role of the autonomic nervous system remains to be tested
The authors discuss the possibility that illuminance and fragrance influenced the autonomic nervous system and thereby saliva secretion. They also consider the way stimulation was delivered and its relationship to neural activity when discussing the unexpected lack of change with a footbath.
What they directly measured was the weight of saliva, not autonomic activity, saliva viscosity, or which salivary glands produced it. Understanding the mechanism would require measuring such indicators at the same time.
It also matters that the sample consisted of a small number of healthy young men. The authors propose future studies involving women, older people, and people with dry mouth. These findings do not establish a treatment for dry mouth or a method for using fragrance at home.
Summary
When fragrance, a footbath, and their combination were tested at two illuminance levels, saliva collected 30–40 minutes after pineapple fragrance alone under low illuminance was greater than before exposure. Fragrance under high illuminance, the footbath, and the combined conditions showed no significant changes over time.
The study provides a specific lead for exploring the relationship between saliva and the living environment. The next steps are to compare changes directly between conditions and to measure mechanisms such as autonomic activity. It leaves an important question: how should fragrance be considered together with its surroundings, rather than on its own?
At the time of the study, four authors were affiliated with the Lion Foundation for Dental Health and three with Chiba University. The original conflict-of-interest section states that the work was a joint study by the two institutions; it is not a declaration of “no conflicts of interest.” No separate funding statement was found.
Reference
Nohara K, Zhang Y, Kasen T, et al. Effects of Environmental Factors on the Amount of Saliva—Study on Illuminance, Fragrance and Footbath—. Japanese Journal of Physiological Anthropology. 2021;26(1):1–7. doi:10.20718/jjpa.26.1_1
