A single swollen nostril is usually caused by something minor, like a small infection at the opening of the nose or the natural alternating congestion cycle your body runs every few hours. Less commonly, it points to a structural issue like a deviated septum or, rarely, a growth that needs medical evaluation. The cause depends a lot on whether the swelling is new or has been there for weeks, and whether you have other symptoms alongside it.
The Nasal Cycle: Normal One-Sided Congestion
Your body naturally shifts airflow between your two nostrils throughout the day. Erectile tissue along your nasal septum and lower turbinate (a bony ridge inside your nose) swells on one side while it shrinks on the other. This means one nostril always carries more air than its partner, and then they swap. The average cycle lasts about two hours while you’re awake, though it can range anywhere from 15 minutes to over 10 hours. During sleep, each side tends to stay dominant longer, averaging around four and a half hours.
Most people never notice this happening. But if you’re paying close attention to your nose because of a cold, allergies, or anxiety, you may suddenly feel that one side seems more blocked. If the swelling alternates sides and you have no pain, discharge, or bleeding, the nasal cycle is the most likely explanation.
Nasal Vestibulitis: Infection at the Nostril Opening
The most common reason for sudden, painful swelling in one nostril is nasal vestibulitis, an infection of the skin just inside the nostril opening. Staphylococcus bacteria are typically responsible. You might notice what looks like a pimple or sore inside the nostril, along with redness, tenderness, itching, and sometimes yellow crusting around the base of the septum. Picking your nose, plucking nose hairs, or frequent nose blowing during a cold can create the tiny skin breaks that let bacteria in.
Mild cases usually clear up with a topical antibiotic ointment applied inside the nostril. More stubborn infections may require oral antibiotics. If you see a growing, increasingly painful lump that doesn’t improve after a few days of keeping the area clean, it’s worth getting checked, since untreated infections near the nose can occasionally spread to deeper tissue.
Deviated Septum and Compensatory Swelling
The septum is the thin wall of cartilage and bone dividing your two nasal passages. When it leans to one side, which is extremely common, the narrower passage is more prone to feeling blocked. The wider side, meanwhile, can develop compensatory turbinate hypertrophy: the turbinate tissue on the roomier side gradually enlarges to fill the extra space. The result is that one nostril feels chronically swollen or stuffy even when you don’t have a cold.
A deviated septum can be something you’re born with or the result of an injury. The swelling it causes tends to be worse during colds or allergy flares, when inflamed tissue narrows an already tight passage further. Noisy breathing during sleep is another common sign. If one nostril has always felt more blocked than the other, a septal deviation is a likely contributor.
Allergies and Turbinate Swelling
Your turbinates warm and humidify incoming air by adjusting their size, swelling to slow airflow or shrinking to let more through. In allergic rhinitis, this system gets hijacked. Exposure to an allergen triggers fluid buildup, increased blood flow, and tissue swelling in the turbinates. Allergic turbinate swelling is usually bilateral (both sides), but a deviated septum can make one side feel dramatically worse than the other, creating the impression that only one nostril is affected.
Vasomotor rhinitis, a non-allergic form of chronic nasal inflammation, works through a similar mechanism. The nerves controlling blood vessel tone in the turbinates become dysregulated, leading to swelling and excess mucus production without any identifiable allergen. Temperature changes, strong odors, and stress are common triggers.
Nasal Polyps: When One Side Matters
Nasal polyps are smooth, soft, grey, semi-translucent growths that develop from the lining of the sinuses and hang into the nasal passage. They can cause a persistent feeling of blockage, reduced smell, and runny nose. The key clinical detail here is that inflammatory nasal polyps are almost always bilateral. A polyp appearing on only one side raises suspicion for something other than routine inflammation, including benign growths like antrochoanal polyps or, less commonly, inverted papillomas or malignant tumors.
This doesn’t mean a one-sided polyp is cancer. It means a one-sided polyp warrants a closer look, typically with a biopsy, to rule out other possibilities.
Red Flags Worth Knowing
The vast majority of one-sided nasal swelling is benign. But certain combinations of symptoms signal that you should get evaluated promptly. Unilateral nasal blockage paired with bloody discharge from one side, facial numbness or pain on one side, or changes in vision (particularly double vision) are considered red flags for sinonasal tumors. Other warning signs include loose teeth without a dental explanation, swelling near the inner corner of the eye, or persistent one-sided nosebleeds.
Any single one of these symptoms in isolation could have an innocent cause. The concern rises when multiple unilateral symptoms cluster together, or when one-sided blockage persists and worsens over weeks without responding to typical treatments.
How Doctors Figure Out the Cause
The first step is usually a nasal endoscopy, a quick in-office procedure where a thin, flexible camera is passed into the nostril. This allows a direct look at the turbinates, septum, and sinus openings, and can identify polyps, infections, or suspicious masses. Endoscopy is effective at spotting mucosal changes, discharge, and growths without any radiation exposure.
A CT scan is the gold standard when surgery is being considered, when a tumor is suspected, or when initial treatment hasn’t worked. It provides a detailed map of the sinuses and any bony involvement. For straightforward cases of infection or allergy-driven swelling, imaging usually isn’t necessary on the first visit.
Managing Swelling at Home
If your swelling seems related to congestion, allergies, or a mild cold, saline irrigation is one of the most effective and low-risk things you can do. Mix three heaping teaspoons of non-iodized salt with one rounded teaspoon of baking soda. Add one teaspoon of this mixture to one cup (8 ounces) of lukewarm distilled or previously boiled water. Tilt your head over a sink, rotate slightly, and gently squeeze the solution into the top nostril, letting it drain from the other side. For general allergy maintenance, once daily to every other day is sufficient. During an active sinus infection, two to three times per day works better.
If the saline stings, use less of the salt mixture. And if you’re also using a nasal steroid spray, wait at least 30 minutes after rinsing before applying it, so you don’t wash the medication right back out.
For a small pimple or sore inside the nostril, keeping the area clean and applying an over-the-counter antibiotic ointment is a reasonable first step. Avoid squeezing or picking at it. If it’s getting bigger, more painful, or developing surrounding redness and warmth after two to three days, an in-person evaluation is the right call.