Do People Without a Sense of Smell Breathe Differently?

When checking a scent, we bring our nose a little closer and take a short breath in. But does everyday breathing also contain movements that explore surrounding odors, even when we are not consciously sniffing?

In a study published in 2024, Gorodisky and colleagues recorded nasal breathing for 24 hours in people born without a sense of smell, a condition called congenital anosmia, and people reporting no problems with smell. They examined not just the number of breaths but also changes in airflow within each breath.

Recording airflow through both nostrils for a day

The participants were 21 people with congenital anosmia and 31 controls. For the former group, the absence of any memory of smelling was supplemented by medical examination, an odor-identification test, MRI, and other assessments. Normal smell in the control group was self-reported and was not confirmed using the same olfactory test.

Participants wore a small recording device with thin tubes connected to both nostrils. It measured pressure changes and converted them into nasal airflow. They continued their normal activities and kept diaries recording, among other things, waking and sleeping times.

The device recorded approximately six times per second, capturing small fluctuations within breaths as well as their overall cycle. It did not measure airflow through the mouth. This was not a study of total breathing volume through the nose and mouth combined.

Breath counts and peaks within a breath are different

When a complete inhalation–exhalation cycle was counted as one breath, there was no statistically clear difference in breathing rate between groups. Both groups breathed more slowly during sleep than while awake.

The difference lay in the number of “peaks,” brief increases in airflow during inhalation. A single inhalation can contain one small peak or several. Four breaths need not contain only four inhalation peaks.

While awake, the control group averaged about 23.8 peaks per minute, compared with about 19.5 in the congenital anosmia group. This difference was statistically significant. A difference of approximately four per minute amounts to roughly 240 per hour.

What increased was not the number of complete breaths but the small inhalation peaks that can occur within a breath. Peak counts during sleep did not differ clearly between groups. The authors considered whether the additional peaks during wakefulness might reflect exploration of surrounding odors.

What happens in a room with few odors?

To provide an additional test of this idea, the researchers measured a separate group of 32 people with normal smell in a room with low-odor materials and high-performance ventilation and filtration. They averaged about 17.2 inhalation peaks per minute, not significantly different from the congenital anosmia group recorded in daily life.

This is consistent with the explanation that interaction with an odorous environment increases small inhalations. However, participants in this control experiment were seated. Their conditions differed from everyday recordings that included walking and other activity, so the difference cannot be attributed to odors alone. Nor was this a comparison in which only the environment was changed for the same people.

Waveforms also differed during sleep

The researchers extracted additional nasal-airflow features besides peak counts. They generated 50 measures across sleep and wakefulness, reduced overlapping information, and compared 27 measures. Group differences remained in four after accounting for chance findings from multiple comparisons.

Besides fewer waking inhalation peaks, the congenital anosmia group had a higher proportion of breaths with a pause after inhalation and smaller maximum expiratory airflow. During sleep, relative variation in inhalation volume from one breath to the next was greater.

The explanation therefore goes beyond less odor exploration during the day. Because differences were also present during sleep, the authors proposed that growing up without smell might alter nasal-breathing patterns themselves. This comparison between groups did not track that developmental process.

Can breathing alone distinguish olfactory status?

The researchers also used the four measures that retained group differences to classify participants. Repeatedly leaving one person’s data out of training and predicting their group produced about 83% classification accuracy among these 52 participants. Classification used nasal airflow alone, without presenting odors.

However, 67% of participants with congenital anosmia and 94% of controls were correctly classified, so the two groups were not identified equally reliably. Validation took place within the population used to select the features. These figures do not establish a diagnostic method validated in a new, independent population.

Variation in inhalation volume during sleep was particularly important for classification; removing it sharply reduced performance. The authors interpreted this as support for nasal-breathing differences extending beyond the number of additional sniffs.

The authors disclosed a patent application relating to anosmia classification using nasal airflow. Some also disclosed patent applications relating to the recording device and financial interests in the company developing it. The paper states that the company was not involved in this study.

Links to health remain a question for future research

The authors also proposed considering changes in nasal breathing, not just odor perception, when studying relationships between smell and health. Because nasal airflow relates to brain activity, they discuss the possibility that different breathing patterns might influence emotion, cognition, or physical state.

This does not mean that the study identified a cause of poorer health. It did not simultaneously measure effects on illness, lifespan, or brain activity, nor test whether changing breathing improves symptoms or health.

The participants had also lacked smell since birth. Whether similar changes occur after smell is lost through infection or injury, and whether they arise immediately or later, remain questions for future research.

Why measuring small fluctuations matters

The measurement method has implications too. When the authors applied smoothing to the recordings, the group difference in inhalation peaks disappeared. Methods retaining only the broad respiratory rhythm may miss the fine detail examined here.

The recording rate itself was also a compromise with power consumption. Faster recording might reveal still finer differences. Both prolonged measurement of nasal airflow in everyday life and preservation of its detail are important.

Conclusion

People with congenital anosmia and controls differed less in overall breathing rate than in small inhalations within breaths and the shape of nasal airflow, including during sleep. Everyday recordings highlight the nose’s dual role in breathing and exploring surrounding odors.

The authors propose studying changes associated with the absence of smell from the perspective of breathing as well as perception. Measurements that preserve fine nasal-airflow detail offer a new way to investigate how smell and breathing interact in daily life.

References

Gorodisky, L., Honigstein, D., Weissbrod, A., Weissgross, R., Soroka, T., Shushan, S., & Sobel, N. (2024). Humans without a sense of smell breathe differently. Nature Communications, 15, 8809. DOI: 10.1038/s41467-024-52650-6 / Full text. Original article: © The Author(s) 2024, CC BY-NC-ND 4.0.