Asymmetrical nostrils, often referred to as alar asymmetry, occur when the openings of the nose appear unequal in size, shape, or height. This difference can range from subtle to noticeable, sometimes affecting the functionality of the airway. A slight degree of nostril unevenness is extremely common across the general population, as perfect facial symmetry is not the biological norm. The causes of more significant asymmetry are tied to factors ranging from how the nose initially developed to external events and acquired conditions over time.
Inherent Structure and Developmental Factors
The most frequent underlying cause of uneven nostrils originates in the developmental structure of the nasal passage, particularly the nasal septum. This thin wall of cartilage and bone divides the two nostrils equally. When the septum develops off-center, a condition known as a deviated septum, it can physically push or distort the surrounding cartilaginous structures, leading to visible asymmetry.
The deviation often involves the caudal septum, the lower, leading edge of the septal cartilage closest to the nostril openings. An off-center caudal septum can cause a secondary bend in the alar cartilages, which form the nasal tip and nostril rim. This structural effect results in one nostril appearing larger or more open than the other.
Beyond the septum, natural genetic variation in the growth of the nasal bones and cartilage can also lead to unevenness. This includes differences in the shape of the medial crura, the cartilage that forms the strip separating the nostrils, which can flare unevenly and cause a size discrepancy. Minor craniofacial development issues, involving growth discrepancies in the facial bony skeleton, have also been linked to nostril asymmetry by influencing the final shape and balance of the nostrils.
Trauma, Prior Surgery, and External Injuries
External physical events that disrupt the nasal framework are a common source of acquired nostril unevenness. A direct impact to the face, such as a sports injury or a broken nose, can displace the delicate bone and cartilage, causing them to heal in an asymmetrical position. Even after a procedure to reset a fracture, the cartilage and bone may not align perfectly, sometimes resulting in a persistent deviated nose.
Prior surgical intervention, known as an iatrogenic cause, can also lead to asymmetry. Rhinoplasty or septoplasty procedures involve manipulating or removing cartilage, and the subsequent healing process can introduce new unevenness. Scar tissue formation (fibrosis) is a major factor, as it may contract unevenly on one side of the nose, pulling the soft tissue and distorting the shape or position of one nostril rim.
In the immediate aftermath of surgery, asymmetric swelling (edema) is a temporary cause where one side retains more fluid. Long-term issues can arise if cartilage grafts shift during the healing process or if excessive cartilage removal destabilizes the structure. Septoplasty, which aims to straighten the septum, can sometimes inadvertently cause deformities like columellar retraction, where the strip of tissue between the nostrils pulls back, altering the nostril’s appearance.
Acquired Medical Conditions Affecting the Airways
A variety of medical conditions that develop over time can lead to a visible difference in nostril size or shape. Nasal polyps, which are soft, noncancerous growths, form in the nasal passages and sinuses due to chronic inflammation. If a polyp or a cluster of polyps grows unilaterally, it creates a localized blockage and pressure that may cause one side of the nose to swell or distort the internal passage, mimicking external asymmetry.
Another common acquired issue is nasal valve collapse, where the cartilage that supports the side wall weakens and collapses inward during inhalation. This condition is often secondary to the aging process, prior surgery, or a pre-existing deviated septum. When external nasal valve collapse occurs on only one side, it makes that nostril appear narrower, or causes it to visibly pinch shut when a person breathes in, creating functional and aesthetic unevenness.
Rarely, a cyst or tumor may develop within the nasal or sinus cavity, physically pushing against the bone and cartilage from the inside. This unilateral growth can lead to progressive distortion of the external nasal contour and nostril size. If a person experiences a sudden or quickly worsening asymmetry, particularly when accompanied by difficulty breathing or persistent pain, seeking medical consultation is important to rule out these more serious acquired conditions.