Inside the nose, a deviated septum looks like the central wall between your two nasal passages bowing, curving, or angling off to one side instead of running straight down the middle. Depending on severity, this shift can range from a subtle lean that barely narrows one airway to a dramatic curve that nearly touches the outer wall of the nostril, blocking it almost completely. Up to 80 percent of people have some degree of off-center septum, though most never notice it.
What the Septum Looks Like Normally
The nasal septum is a thin, flat wall that divides your nose into two roughly equal passages. The front portion is made of flexible cartilage, which is why the tip of your nose has some give when you press on it. Farther back, the septum transitions to bone: the perpendicular plate of the ethmoid bone near the top and the vomer bone lower down, with a ridge of the maxilla (upper jaw bone) running along the floor. In a perfectly straight septum, this entire structure sits right along the midline, giving both nostrils about the same amount of airspace.
How a Deviation Changes the View
When a doctor looks inside the nose with a lighted scope or a simple nasal speculum, a deviated septum is visible as the central wall leaning, bulging, or curving into one nasal passage. The most common shapes are a C-curve, where the septum bows smoothly to one side along its length, or an S-curve, where the upper portion bends one direction and the lower portion bends the other, narrowing both sides at different points.
The deviation can occur in the cartilage at the front of the nose, the bone toward the back, or both. Cartilage deviations tend to produce a smooth, rounded bulge you can sometimes feel with your finger just inside the nostril. Bony deviations farther back often look more angular, sometimes forming a sharp ridge or spur that juts into the airway. These bony spurs can be especially noticeable on imaging and can press against the side wall of the nose.
On the narrowed side, you’d see the septum crowding into the airway, reducing the visible space to a slit in severe cases. On the wider side, the passage looks more open than normal.
Severity by How Much Airway Is Blocked
Clinicians grade deviations by how much of the nasal passage they obstruct. A mild deviation blocks roughly one-third of the airway on the affected side. A moderate deviation blocks about two-thirds. A severe deviation essentially closes the passage off entirely, with the septum touching or nearly touching the outer nasal wall. Many people with a mild deviation breathe fine and never need treatment; it’s the moderate-to-severe range that typically causes persistent one-sided congestion, mouth breathing, or recurring sinus problems.
Interestingly, the severity of the physical deviation doesn’t always match how blocked someone feels. Studies have found that the degree of visible or measurable deflection on the septum doesn’t reliably predict how much nasal obstruction a person experiences day to day. Swelling, allergies, and other soft tissue factors play a significant role in how much airflow actually gets through.
What Happens on the Opposite Side
One of the more surprising things about a deviated septum is what it does to the other nostril. Inside each nasal passage, there are curved, shelf-like structures called turbinates that warm and humidify the air you breathe. When the septum pushes into one side and opens extra space on the other, the body compensates. The inferior turbinate on the wider side gradually enlarges to fill that extra room, a process called compensatory hypertrophy.
This means that when a doctor looks inside the “open” side of the nose, they often see a swollen, bulky turbinate taking up much of the space. The enlargement involves both the soft mucosal lining (especially the inner surface facing the septum) and the underlying bone of the turbinate itself. This is a permanent structural change, not temporary swelling that comes and goes with allergies. The result is that both sides of the nose can feel blocked: one from the septum itself, the other from the enlarged turbinate responding to it.
What You Can See Versus What You Can’t
A deviated septum is not always visible from the outside. Some people with a significant internal deviation have a nose that looks perfectly straight externally, because the deviation occurs deeper in the cartilage or in the bony portion toward the back of the nasal cavity. Others have an obviously crooked nose that clearly signals the septum beneath is off-center. The only reliable way to assess the deviation is to look inside, either with a scope in an ENT office or, when other problems like sinus disease are suspected, with a CT scan.
On a CT scan, the deviation shows up clearly as the septum line curving away from center. Radiologists can see exactly where the deflection occurs, whether it’s in the cartilage, bone, or both, and whether a bony spur is present. CT scans also reveal whether the deviation is affecting drainage pathways to the sinuses. That said, imaging isn’t necessary for a straightforward deviation. A doctor can usually see everything they need with a direct look inside the nose.
Mucosal Contact Points and Irritation
In moderate and severe deviations, the septum can press directly against the turbinates or the outer wall of the nasal passage. These contact points are visible during an exam as areas where the tissues on both sides are compressed together. The mucosa at these spots often looks red, irritated, or swollen from the constant pressure. In some cases, the friction and pressure at contact points contribute to headaches or facial pain, particularly around the bridge of the nose or behind the eye on the affected side.
The mucosa on the convex (bulging) side of the deviation tends to be drier and more exposed to airflow, making it prone to crusting and nosebleeds. On the concave (narrowed) side, airflow is restricted and mucus drainage slows down, which can create a breeding ground for recurring infections.