When sick with a cold or flu, many people experience one nostril feeling completely blocked, making breathing difficult. This common sensation results from a combination of normal physiological processes and the body’s immune response to infection. This article explores the biological mechanisms behind this uneven nasal congestion.
The Nasal Cycle
The alternating blockage and clearing of nostrils is not solely a symptom of illness; it is a natural, continuous process known as the nasal cycle. Even in healthy individuals, nasal passages do not remain equally open throughout the day. One nostril typically becomes more congested while the other clears, with this pattern switching every few hours.
This cycle results from changes in blood flow to the erectile tissues lining the nose. As blood flow increases to one side, the tissues swell, temporarily reducing airflow, while the opposite side becomes more open. This alternating dominance prevents nasal passages from drying out and allows each nostril a period of rest from constant airflow and filtration.
How Illness Exaggerates Nasal Congestion
When the body encounters a pathogen, such as a cold virus, it initiates an immune response that directly impacts the nasal passages. This response increases blood flow to the affected area, bringing immune cells to fight infection. This leads to inflammation, causing the tissues lining the nose to swell significantly.
This inflammatory swelling, when superimposed on the normal nasal cycle, amplifies the feeling of blockage. The nostril already in its naturally more congested phase becomes even more obstructed due to the added inflammation. This combination can result in one nostril feeling completely closed off, making breathing difficult. Additionally, the body increases mucus production as part of its defense, and this excess mucus further contributes to congestion by physically blocking the swollen nasal passages.
Key Physiological Players
The anatomical structures responsible for the nasal cycle and its exaggeration during illness are the turbinates, also known as conchae. These bony structures inside the nasal cavity are covered by a rich mucous membrane and extensive blood vessels. Turbinates can rapidly swell and shrink due to their highly vascularized tissue, which engorges with blood.
Blood flow to these turbinates is controlled by the autonomic nervous system, specifically its sympathetic and parasympathetic branches. The sympathetic nervous system constricts blood vessels, leading to turbinate shrinkage and increased airflow. The parasympathetic nervous system promotes vasodilation, causing turbinates to swell and reduce airflow. During illness, the immune response triggers signals favoring parasympathetic activity and inflammatory processes, leading to pronounced turbinate swelling and characteristic one-sided nasal congestion.