Feeling unable to breathe through one side of the nose, such as the left nostril, is a common complaint known as unilateral nasal obstruction. This one-sided blockage can be disruptive, affecting sleep quality and comfort. While temporary congestion is minor, persistent blockage suggests a focused physiological or anatomical cause. Understanding this requires looking into the body’s normal functions, temporary inflammatory responses, and permanent structural variations.
The Physiological Explanation
The nasal cycle, a completely normal process, often creates the feeling of a one-sided blockage. Controlled by the autonomic nervous system, the cycle involves the alternating congestion and decongestion of the nasal cavities. This system dictates blood flow to the turbinates, which are bony structures covered by erectile tissue within the nasal passages.
In 70 to 80% of adults, the turbinates on one side swell slightly, restricting airflow, while the turbinates on the opposite side shrink, allowing for clearer breathing. This switch typically occurs every two to six hours. This alternating process is a protective mechanism, allowing the mucous membranes on the congested side to rest and maintain optimal function for filtering and humidifying air. If a person is focused on their breathing, this normal physiological shift can become noticeable and mistakenly perceived as a blockage.
Congestion from Inflammation and Infection
Beyond the nasal cycle, the most frequent causes of unilateral blockage are temporary conditions involving inflammation and increased mucus production. Common illnesses like the cold or flu cause the lining of the nasal passages to swell, narrowing the airway. Acute sinusitis, the inflammation of the sinus linings, can also create one-sided pressure and obstruction if the infection is localized to a single sinus cavity.
Inflammatory responses can be asymmetrical, meaning they affect one nostril more than the other. Allergic rhinitis causes the release of histamine, which leads to swelling and excess fluid production in the nasal tissues. If a person sleeps on their side, gravity can cause a pooling of inflammatory fluid, exacerbating the congestion in the lower nostril.
Anatomical Reasons for Unilateral Blockage
When the inability to breathe through the left nostril is chronic and persistent, the cause is often a fixed anatomical issue. The nasal septum, the wall of cartilage and bone that divides the nose into two passages, is rarely perfectly straight. A deviated septum occurs when this wall is displaced to one side, such as the left, physically blocking the airway. This deviation can be present from birth or result from an injury to the nose.
Another common structural cause is turbinate hypertrophy, which is the chronic enlargement of the turbinates, most often the inferior turbinates. While turbinates normally swell and shrink, chronic inflammation from allergies or environmental irritants can cause them to become permanently enlarged. A deviated septum can sometimes cause the turbinate on the opposite side to become hypertrophied in a compensatory effort to regulate airflow.
Less frequently, unilateral blockage can be caused by a nasal polyp, a non-cancerous growth in the nasal or sinus lining. While polyps often occur bilaterally, a single large polyp or cluster in the left nasal passage will physically obstruct airflow. Other causes include a foreign body, particularly in children, or a benign or malignant tumor. These present as a stubborn, one-sided blockage that does not respond to standard medical treatment.
Seeking Professional Diagnosis and Treatment
A persistent, unilateral nasal obstruction that lasts longer than several weeks warrants a medical consultation. It is particularly important to seek professional help if the blockage is accompanied by symptoms such as recurrent nosebleeds, facial pain, changes in vision, or a watery, clear discharge that may indicate a cerebral spinal fluid leak, as these signal a more serious underlying issue.
Diagnosis
A medical provider will typically begin with a physical examination of the nasal passages using a lighted instrument called an anterior rhinoscopy. To get a more detailed view of the posterior nasal cavity and the sinus drainage pathways, they may perform a nasal endoscopy, which uses a small, flexible camera.
Treatment
Treatment is focused on the underlying cause. If inflammation is the issue, medical management like corticosteroid nasal sprays or antihistamines can be effective. If the persistent blockage is due to a severe deviated septum or large polyps, surgical intervention, such as a septoplasty or turbinate reduction, may be necessary to restore adequate airflow.