Differences in the size or shape of the nose holes (nares) are known as nasal asymmetry. Perfect symmetry is rare in the human body, and the nose, positioned centrally on the face, often exhibits slight variations. These minor differences are usually harmless, resulting from a combination of developmental factors, internal physiological processes, and structural changes. Understanding these common reasons clarifies why nostrils may not look identical.
Normal Variation and Developmental Factors
Slight nasal asymmetry begins during facial and skull development. The nasal structure forms from the merging of multiple facial components, and the growth of underlying cartilage and bone is rarely perfectly mirrored. This natural variation results in differences in the size and contour of the external nostrils from a young age.
Beyond fixed structure, the size of breathing passages changes constantly due to the nasal cycle. This unconscious, alternating cycle involves the turbinates—finger-like projections containing erectile tissue—periodically swelling and shrinking. The cycle directs the majority of airflow through one nostril for a period, typically lasting half an hour to several hours, before alternating sides. This cyclical congestion temporarily alters the inner volume, which can make one nostril appear more open than the other at any given moment.
The Primary Structural Cause: Deviated Septum
The most frequent structural reason for uneven nostrils is a deviated septum, a condition estimated to affect up to 80% of the population. The nasal septum is a thin wall of cartilage and bone that ideally divides the nasal cavity into two equally sized passages. When this wall is significantly off-center, it is called a deviation.
A severely deviated septum physically bows into one nasal passage, constricting the internal area and restricting airflow. This displacement can push surrounding tissues, making the outer nostril on the opposite, unobstructed side appear larger or more open. Deviation can be present at birth, often due to the septum growing faster than the surrounding facial structure, or it can result from trauma later in life.
Acquired and Dynamic Contributors
Factors other than fixed developmental anatomy contribute to both permanent and temporary asymmetry. Even minor impacts to the nose, particularly during childhood or contact sports, can subtly shift the delicate nasal cartilage structure. These small injuries may not result in a broken nose but can cause the cartilage framework to heal in a slightly misaligned position. This acquired change influences the shape of the external nares and internal passages.
Temporary swelling of the nasal lining also alters nostril size and airflow. Conditions like allergies, common colds, or chronic sinusitis cause the turbinates to become inflamed and enlarged (turbinate hypertrophy). Since this swelling may not be symmetrical, one nasal passage can be more blocked than the other, making the less congested nostril appear larger or clearer. Furthermore, long-term differences in how a person uses facial muscles, which attach to the soft tissues of the nose, can gradually influence the shape and position of the external nostril rim.
When Asymmetry Becomes a Health Concern
While minor cosmetic asymmetry is normal, the difference in nostril size becomes a concern when it impairs nasal airway function. Chronic difficulty breathing through one side of the nose is the primary indicator for seeking professional evaluation. This persistent blockage is noticeable during exercise or while sleeping, often leading to mouth breathing, snoring, or other sleep disturbances.
Other signs that warrant consultation with a physician, such as an ear, nose, and throat (ENT) specialist, include frequent nosebleeds or recurrent sinus infections. Nosebleeds can occur when uneven airflow dries out the septum on one side. If the breathing impairment is severe and linked to a physical obstruction like a deviated septum, procedures such as a septoplasty may be recommended to straighten the internal structure and restore proper airflow.