A recent study published in Nature Communications has uncovered that individuals with congenital anosmia—a condition where a person is born without the ability to smell—exhibit altered patterns of nasal breathing compared to those with a normal sense of smell. These differences persist during both waking hours and sleep, and the findings suggest that disrupted airflow may play a role in some of the health challenges associated with anosmia.
While the human sense of smell is often undervalued, its loss can significantly reduce quality of life. People with anosmia commonly report emotional difficulties, dietary changes, and even a higher risk of mortality. Despite these serious outcomes, the underlying reasons remain unclear. Researchers have long known that the human nose serves two functions: smelling and breathing. Odors influence how we breathe—for example, unpleasant smells often cause us to inhale less deeply. Given this connection, the researchers hypothesized that individuals with anosmia might experience altered patterns of nasal airflow. These changes, they speculated, could contribute to the negative health outcomes associated with anosmia.
To test their hypothesis, the researchers used a wearable device capable of measuring nasal airflow with high precision. This device logged data continuously over 24 hours and recorded subtle variations in breathing patterns.
The study involved two groups: 21 participants with isolated congenital anosmia (no sense of smell since birth) and 31 participants with a normal sense of smell. The researchers ensured that participants with anosmia had no other medical issues causing their condition, such as trauma or sinus disease. Each participant’s sense of smell was confirmed using a standardized test, and those with anosmia also showed a lack of olfactory bulbs—structures in the brain responsible for processing smell.
Participants wore the device during their usual daily activities and kept a diary to track their sleep and wake times. Using this data, the researchers analyzed patterns of nasal airflow, focusing on differences between those with and without anosmia.
The results showed significant differences in nasal airflow between the two groups. While the overall breathing rate—measured in breaths per minute—was similar, the patterns within each breath were notably altered in individuals with anosmia.
One key finding was that people with a normal sense of smell displayed a higher number of “inhalation peaks” during the day. Inhalation peaks refer to subtle bursts of air intake within a single breath, which likely reflect sniffing—a natural behavior used to explore and respond to smells. On average, individuals without anosmia had about 240 more inhalation peaks per hour while awake compared to those with anosmia. Interestingly, when people with a normal sense of smell were placed in an odor-free environment, their breathing patterns resembled those of individuals with anosmia. This suggests that the increased inhalation peaks in people with normal olfaction are driven by their interaction with environmental smells.
The study also found differences in other respiratory features. Individuals with anosmia showed:
- More frequent pauses during inhalation while awake.
- Lower exhalation flow rates during wakefulness.
- Greater variation in the volume of air inhaled during sleep.
These findings indicate that anosmia is associated with altered nasal airflow patterns that persist even during sleep, when smell plays a minimal role.
The researchers further tested whether these breathing differences could be used to classify anosmia. Using machine learning, they entered the most significant respiratory parameters into a model and achieved an impressive 83% accuracy in distinguishing participants with anosmia from those with a normal sense of smell.
The findings offer a new perspective on how anosmia might impact health. Since nasal airflow influences brain activity, emotion, and cognition, the altered breathing patterns seen in anosmia could have far-reaching consequences. For example, sniffing behaviors, which appear reduced in anosmia, are thought to help regulate brain activity, particularly in regions related to attention and memory. Additionally, irregular airflow during sleep could affect overall respiratory health.
However, the study has some limitations. For one, the device measured only nasal airflow, not mouth breathing, which may have provided a more complete picture of respiratory patterns. The study also relied on participants’ self-reported activities, which may introduce minor inaccuracies. Additionally, while the research highlights differences in airflow, it cannot determine whether these changes directly cause the health issues associated with anosmia. Future studies could compare individuals with congenital anosmia to those who develop anosmia later in life to explore how breathing patterns evolve over time.
Despite these limitations, the study provides evidence that the absence of smell affects how people breathe. The altered respiratory patterns observed in anosmia may help explain why this condition is linked to broader health challenges. By revealing a new connection between smell and breathing, the study challenges the idea that olfaction is an “unimportant” sense and opens the door to further research into the far-reaching effects of nasal airflow on health and behavior.
The study, “Humans without a sense of smell breathe differently,” was authored by Lior Gorodisky, Danielle Honigstein, Aharon Weissbrod, Reut Weissgross, Timna Soroka, Sagit Shushan, and Noam Sobel.
