When sustained arithmetic makes you tense, could an apple-like fragrance change your heart’s response? In a study of 25 healthy male university students, the rise in heart rate during the task was smaller with a formulated apple fragrance than with either an unscented control or a formulated chamomile fragrance.
Meanwhile, nose-tip temperature, perceived workload, and arithmetic performance did not change in the same way as heart rate. One key to reading this study is that the apparent effect of a fragrance depends on which bodily response is measured.
- Apple fragrance and short-term arithmetic stress
- The stimuli were formulated apple and chamomile fragrances
- Measuring heart rate and fluctuations between beats
- Cardiac responses were smaller with apple fragrance
- Nose-tip temperature did not follow the same pattern
- Boredom decreased, but arithmetic performance did not change
- The conditions under which the findings were obtained
- Summary
Apple fragrance and short-term arithmetic stress
The team investigated how apple fragrance relates to short-term physiological responses to a cognitive task. They measured cardiac activity alongside peripheral responses associated with blood flow in the skin.
The participants were 25 healthy male university students with a mean age of 22. Each experienced apple, chamomile, and control conditions on separate days. Condition order was counterbalanced across participants to reduce order effects.
Each session consisted of ten minutes of rest, 30 minutes of arithmetic, and 15 minutes of recovery. The task required continuously adding single-digit numbers displayed on a screen as quickly and accurately as possible. Fragrance was presented only during the task, not during rest or recovery.
The stimuli were formulated apple and chamomile fragrances
The fragrances were prepared by a perfumer, rather than being essential oils extracted from apples or chamomile. The apple formulation included butyl acetate, hexyl acetate, geranyl acetate, and Verdox, while the chamomile formulation included limonene, linalool, geraniol, and Hedione.
The fragrances were prepared in the odorless solvent DPG, with DPG alone as the control. Chamomile provided a comparison with another generally liked odor, rather than limiting the comparison to fragrance versus no fragrance.
A specialized device delivered fragrance through a tube below the nostrils during the first 20 seconds of every minute, followed by a pause. This method aimed to reduce adaptation from continuous smelling and standardize exposure time. It differs from the way odor reaches the nose when a room fragrance is placed indoors.
Measuring heart rate and fluctuations between beats
Electrocardiograms were used to calculate heart rate per minute and heart rate variability, the small fluctuations in the intervals between successive beats. Here, the high-frequency component, HF, served as an index of vagal, or parasympathetic, involvement in cardiac regulation.
An increase in heart rate and a decrease in HF under a demand such as arithmetic suggest a change in cardiac regulation during the task. However, lower HF relates to reduced parasympathetic influence; it is not a direct measure of sympathetic activity.
A temperature sensor was also attached to the nose tip. Because nasal skin temperature can reflect changes in blood flow, it served as a supplementary measure of peripheral responses. Physiological data were adjusted for individual differences and compared against the initial resting period.
Cardiac responses were smaller with apple fragrance
In the unscented DPG and chamomile conditions, heart rate increased and HF decreased during arithmetic relative to rest. In the apple condition, differences between rest and the task were not significant.
The direct comparisons between conditions are important. The increase in heart rate with apple was smaller than with DPG (p = 0.008) and chamomile (p = 0.001). The decrease in HF was also smaller than with DPG (p = 0.029) and chamomile (p = 0.006).
Thus, the finding was not merely that apple alone showed no significant difference from rest: task-related cardiac changes were smaller than in the other two conditions. Chamomile and DPG did not differ significantly on these measures.
Nose-tip temperature did not follow the same pattern
Nose-tip temperature was lower during the task than at rest in the apple and DPG conditions. Between conditions, apple produced a lower temperature than chamomile, but the difference between apple and DPG was not significant.
A smaller cardiac response therefore did not mean that every bodily measure, including skin temperature, shifted in a calming direction. The authors also state that the biological reason for the different cardiac and peripheral findings remains unclear.
Nose-tip temperature is an indicator related to blood flow and other factors in one part of the body. Combined with heart rate variability, it offers a more multidimensional view, but a single temperature change cannot determine the state of the entire autonomic nervous system.
Boredom decreased, but arithmetic performance did not change
In fragrance questionnaires, apple was rated more comfortable, preferable, and intense than DPG. The results did not establish that it was significantly preferred over chamomile.
Seven items assessed mood and perceived demands before and after the task. Changes in boredom were lower with both apple and chamomile than with DPG. In contrast, the fragrance conditions did not show clear differences in tension, effort, concentration, fatigue, irritation, or monotony.
There were also no significant differences in arithmetic accuracy or speed between conditions. Changes in cardiac measures should not be equated directly with an overall improvement in perceived stress or greater work efficiency.
The conditions under which the findings were obtained
The sample was limited to healthy young men, and the stressor was a 30-minute simple arithmetic task. The findings apply to the particular formulations, concentrations, and intermittent delivery to the nose used here. Further testing is needed before extending them to other apple fragrances or everyday room scenting.
The study did not compare formulation ingredients individually, so it cannot identify which ingredients contributed to the results. Relationships between subjective comfort and physiological responses, as well as the influences of expectations and experience, also remain to be disentangled.
Summary
In an experiment where 25 participants experienced three conditions, intermittent apple-fragrance delivery during arithmetic produced a smaller heart-rate increase and HF decrease than both DPG and chamomile. This suggests that fragrance can influence cardiac responses to a short-term task.
Meanwhile, nose-tip temperature did not differ significantly between apple and DPG, and arithmetic performance did not change. Reduced boredom was seen with both apple and chamomile. By distinguishing cardiac, peripheral, and subjective measures, the study provided a more specific picture of fragrance effects.
The research was supported by Nagaoka University of Technology and Takasago International Corporation. Takasago provided partial funding and the fragrances. The paper discloses that coauthor K. Ito was a company employee at the time of the research and received a salary.
References
Dilrukshi EAC, et al. (2024). Alleviation of physiological stress response by apple aroma. Australian Journal of Psychology, 76(1), 2401022. Original paper.
