It is common to feel as though one nostril is more open than the other at any given time. This is a real and normal physiological process, an alternating dominance in nasal airflow that most people experience.
The Nasal Cycle: A Natural Phenomenon
The alternating partial congestion and decongestion of the nasal cavities is known as the nasal cycle. This regular, unconscious pattern causes one side of the nose to become more open for breathing while the other side becomes more restricted. Most healthy adults (70-80%) experience this cycle. While often unnoticed, it can become more apparent during a cold, allergies, or other conditions that increase nasal congestion.
The Underlying Physiology
The nasal cycle is made possible by specialized structures within the nasal passages called turbinates, also known as nasal conchae. These are bony projections covered by a thick, vascularized mucous membrane containing erectile tissue. Similar to other erectile tissues, the turbinates can swell and shrink due to changes in blood flow. When blood flow to the turbinates on one side increases, they engorge with blood, causing that nostril to become more congested and restricting airflow. Simultaneously, the turbinates in the opposite nostril decongest as blood is shunted away, allowing for increased airflow through that side.
This alternating congestion and decongestion is regulated by the autonomic nervous system, which controls involuntary bodily functions. The sympathetic nervous system causes vasoconstriction, leading to decongestion and increased airflow, while the parasympathetic nervous system causes vasodilation, leading to congestion. This interplay of blood vessel constriction and dilation, primarily in the inferior turbinates, orchestrates the continuous shift in nasal airflow. The cycle’s mean duration is approximately two and a half hours, but it can range from 30 minutes to up to six hours.
Why Your Nostrils Take Turns
The nasal cycle serves several biological purposes that contribute to nasal health and function. One primary benefit is maintaining the health of the nasal lining. By alternating airflow, the nasal cycle prevents excessive drying of mucous membranes, allowing cilia (tiny hair-like structures that clear debris) to rest and remain effective. This also ensures proper humidification and filtration of incoming air.
The alternating airflow also optimizes the sense of smell (olfaction). Different odor molecules bind to olfactory receptors at varying speeds. The nasal cycle creates a disparity in airflow, with one nostril having faster airflow and the other having slower airflow. This allows the nose to detect a wider range of smells; some odors are better perceived in faster air, while others are better detected in slower, more prolonged exposure. This enhances overall olfactory sensitivity and range.
Factors Affecting Nasal Airflow
Various internal and external factors can influence the nasal cycle and how noticeably it is perceived. Common illnesses like colds and allergies cause nasal mucosa inflammation, leading to increased congestion and making the cycle more apparent. Changes in body position, such as lying on one side, can also cause the dependent nostril to become more congested.
Physical exercise typically leads to decongestion of the nasal passages, increasing overall airflow. Emotional states like stress or fear can also influence the autonomic nervous system’s control over nasal blood flow, potentially altering the cycle. While the nasal cycle is a normal physiological process, conditions like a deviated septum or enlarged turbinates can lead to a more consistent blockage in one nostril, making the natural cycle feel more pronounced or uneven.