Start with the thing that surprises most people: you almost certainly cannot tell by looking in the mirror, and neither can your GP with a torch.
The nasal septum is the wall dividing your two nasal passages, made of cartilage at the front and bone further back. It runs the full depth of your nose, and the deviations that actually matter are usually higher up and further back than any light source can reach from the outside. A torch shows you the front two centimetres. The clinically important bends frequently sit behind that.
So the honest answer to "how do I know if I have a deviated septum" is that you can build a strong suspicion from your symptoms, confirm nothing from the mirror, and get a definitive answer in about a minute with a camera.
Here is how to build the suspicion.
What does a deviated septum look like from the outside?
Usually, nothing at all.
This is the single biggest misconception I meet. People assume a deviated septum means a visibly crooked nose. Plenty of people with perfectly straight-looking noses have significantly deviated septa, and plenty of people with slightly crooked noses have septa that are fine.
The two are related but separate. The septum is internal. The visible shape of the nose is made by the cartilage and bone on the outside. An injury can bend one, the other, or both. If your nose looks bent from the front, that raises the odds that the septum is bent too, and it changes which operation would help you, but a straight-looking nose rules nothing out.
Which symptoms point to a deviated septum?
Four features, and the more of them you have, the stronger the case.
One side is consistently worse than the other. This is the most useful single sign. Not "it swaps", but the same side being reliably the harder one over months and years. Structural narrowing does not move.
It never fully clears. Even on your best day, in your best season, away from pets and pollen, the nose is not properly open. Allergy fluctuates. Cartilage does not.
Sprays have made only a small difference. Provided they have been used properly, which I will come back to.
It is worse lying down, and worse on the side you lie on. Everyone's nose narrows when horizontal. Only a nose that is already narrow turns that into a problem.
Add a history of any nasal injury, however trivial and however long ago, and the picture firms up considerably. Most septal deviations trace back to something, though many people genuinely cannot recall an injury and a fair number are simply born with one.
The symptoms nobody connects to their septum
Blockage is the headline. It is not the whole story, and the rest of it is why this is worth sorting out rather than living with.
Recurrent sinus infections. This is the one most people miss entirely. The septum forms one wall of the nasal cavity, and a deviation sitting up against the middle turbinate narrows the corridor your sinuses drain through. Mucus that cannot clear gets infected. If you have had several courses of antibiotics for sinusitis in the past couple of years, take that as a pointer rather than bad luck. Antibiotics treat the infection, not the reason it keeps coming back.
Facial pain and pressure. Typically across one cheek or behind the eye on the blocked side. Where a bony spur makes contact with a turbinate it can produce a dull one-sided headache that eases when the lining is decongested.
Nosebleeds. Airflow accelerates over the prominent part of a deviation and dries the lining there. Dry lining cracks and bleeds. Repeated bleeds from the same nostril are worth reporting.
Crusting and post-nasal drip. Same mechanism. Air travels turbulently rather than smoothly, so parts of the nose dry out while others stay wet.
Ear symptoms. Fullness, popping, one ear that will not clear. A word of caution, because this one gets overstated: recurrent ear infections in an adult are rarely down to the septum, and if you have been told they are, ask for the reasoning. Congestion high in the nose can affect how well the Eustachian tube ventilates the middle ear, which is a different and milder problem from infection.
Everything downstream of mouth breathing. Dry mouth on waking, a sore throat first thing, snoring, broken sleep and the daytime fatigue that follows. A fair number of patients come to me about the tiredness and never mention their nose at all.
None of these prove anything on their own. Together they build a case worth investigating.
How can I check for a deviated septum at home?
Of all the self-tests circulating online, two tell you something real.
Alternate nostril occlusion. Press one nostril closed and breathe in through the other. Then swap. Do it standing, calmly, several times over a few days, at different times of day. You are looking for a consistent asymmetry, not a one-off. If the same side is always the poorer one, that is meaningful. If it alternates, you are probably feeling the normal nasal cycle rather than a fixed narrowing.
The cheek pull. Place a fingertip on your cheek beside your nose and pull gently outwards and upwards, then breathe in. If that produces an obvious improvement, the narrowest point of your airway is the nasal valve, just inside the nostril, rather than the septum further back. This is a version of what we call the Cottle manoeuvre. It matters because valve narrowing and septal deviation need different operations, and a positive result here changes the plan.
A related clue: if a nasal strip across the bridge of your nose makes a noticeable difference, that also points at the valve.
Self-checks that tell you nothing
Looking up your own nostrils. You will see the very front of the septum, which is rarely where the problem is.
Photographs of your face. These tell you about the external shape, not the internal wall.
Feeling inside with a finger. You can reach the front edge of the septum and nothing else, and you risk a nosebleed.
Online quizzes and self-test videos. They ask the same symptom questions above, then conclude you might have a deviated septum. You already know that.
The thing that muddies every self-assessment
Almost everyone who has been blocked for years has tried nasal sprays and concluded they did not work. That conclusion is unreliable for two reasons.
Most people use steroid sprays wrongly. It should go in with the head tilted slightly forward, aimed outwards towards the cheekbone on the same side, using the opposite hand, without sniffing hard afterwards. Aimed up the middle it hits the septum, which achieves nothing and causes nosebleeds. And it needs several weeks of daily use before it can be judged, because it is not a rescue treatment.
Second, and more important, decongestant sprays such as xylometazoline and oxymetazoline cause rebound swelling if used beyond about a week. If you have been on one for months, your nose is now blocked partly because of the spray. Nothing can be assessed honestly through that, and it is reversible. Stopping is unpleasant for a fortnight and then most people are better than they were.
So before you conclude your problem must be structural, the fair test is one correctly used steroid spray, daily, for around eight weeks, alongside saline rinses, with any decongestant spray stopped. If that genuinely fails, the case for a structural cause is strong.
Could it be something other than the septum?
Yes, and this is exactly why the camera examination earns its keep. A blocked nose has a short list of usual suspects, and they need different treatment from each other.
Swollen turbinates. The turbinates are shelves of tissue on the side walls of the nose that warm and humidify the air you breathe. Their lining swells with allergy, irritation and infection, and when it swells the nose blocks. The pattern is different from a septal deviation: it fluctuates, it often switches sides, and it responds to a properly used steroid spray. In practice the two frequently coexist, because the turbinate on the wider side of a deviated septum tends to enlarge to fill the space.
Nasal valve narrowing. The narrowest segment of the whole airway sits just inside the nostril, and if it is weak or tight, no amount of septal surgery further back will fix the blockage. That is what the cheek pull test above is screening for.
Rebound congestion from decongestant sprays. Covered above, and worth repeating because it is so common: a nose that has been on xylometazoline for months is blocked partly by the spray itself.
Nasal polyps. These are soft swellings of inflamed lining that block both sides and usually blunt the sense of smell. They are a different disease with a different treatment pathway, and one of the things I am specifically looking for with the camera.
A nose that is bent outside as well as in. After a significant injury the septum and the external framework are often both off line. Straightening the septum alone can leave the outer sidewalls still pushed over and the airway still narrow. In that situation the operation that deals with both at once is a septorhinoplasty, and it is a different undertaking from a septoplasty, with different recovery and different costs.
The point of listing these is not to send you down another rabbit hole. It is that "blocked nose" is a symptom, not a diagnosis, and the examination that tells them apart takes minutes.
How is a deviated septum diagnosed properly?
It is quicker and less unpleasant than people expect.
I use a flexible nasendoscope, a slim fibre-optic camera about four millimetres across, passed through the nostril after a spray of local anaesthetic and decongestant. It takes roughly a minute per side. It shows the whole length of the septum, both sets of turbinates, the sinus openings and the back of the nose. Most people ask to watch on the screen, and most are surprised when they see their own anatomy for the first time.
I also look before and after decongestion. The difference between those two views answers the question that actually decides your treatment: how much of your blockage is swelling, which medication can fix, and how much is structure, which it cannot.
If surgery is on the table, I usually request a low-dose CT of the sinuses. That confirms the shape and extent of the deviation, shows any sinus disease, and rules out the less common conditions that can mimic a deviated septum.
If there is any allergic pattern, testing is worth doing rather than guessing. Treating structure while ignoring allergy, or the reverse, is the commonest reason people end up disappointed.
What happens if it is confirmed
Having a deviated septum is not in itself a reason to operate. A perfectly straight septum is close to non-existent, so finding a bend on a scan proves very little on its own. The question worth answering is not whether your septum is deviated but whether the deviation explains your nasal congestion. Those are two different questions and only one of them decides anything.
The UK evidence here is unusually good. The NAIROS trial, run across seventeen NHS hospitals and published in 2024, found a large benefit from septoplasty in people with moderate to severe symptoms, and very little benefit in those with mild ones. That is worth knowing before you decide anything: if your symptoms are mild, an operation is a marginal intervention. What should decide it is the effect on your quality of life, not the severity of the bend.
Surgery for a deviated septum, a septoplasty, straightens the wall under a general anaesthetic. It is one option among several, and in a fair number of cases it is not the one I would start with. Where the airway also narrows at the valve, septum surgery on its own underdelivers, which is why the cheek pull test above earns its place.
I have written the full picture on symptoms, the treatment ladder, the NAIROS data, what the operation involves and what it costs in my main guide: deviated septum, symptoms, surgery and recovery. If you want to know whether it can be sorted without an operation, that is covered separately in can you fix a deviated septum without surgery.
Frequently asked questions
What does a deviated septum look like?
From outside, usually nothing. Inside, the dividing wall sits off centre, often as an S-shaped curve or a spur of bone projecting into one passage. It is only visible with a camera or on a scan.
Does a deviated septum always cause symptoms?
No. A large number of people have one and never notice. That is exactly why the diagnosis alone does not justify surgery.
Can a deviated septum develop over time?
The deviation itself changes little after growth finishes. What changes is the lining around it, and the nose droops slightly with age, both of which can make a long-standing deviation start to feel worse in your forties and fifties.
Can I have a deviated septum without ever breaking my nose?
Yes, and it is common. Many are developmental, arising as the nose grows. Others follow injuries too minor to remember.
Does a deviated septum cause snoring?
It can contribute, by forcing mouth breathing. It is rarely the whole explanation, and it is not the same thing as sleep apnoea.
Can a deviated septum cause sinus infections?
Yes, indirectly. A deviation that narrows the drainage pathway means mucus sits rather than clears, and stagnant mucus gets infected. Recurrent sinus infections on one side in particular should prompt a proper look inside.
Can a deviated septum cause ear problems?
It can cause pressure and popping by affecting how the Eustachian tube ventilates. It is a poor explanation for recurrent ear infections in an adult, and I would want another cause excluded before accepting that one.
If one nostril is smaller on the outside, does that mean a deviated septum?
Not reliably. External nostril asymmetry is extremely common and often unrelated to the internal septum.
Do I need to see a specialist, or will my GP do?
Your GP can start the medical treatment and should, because that has to be tried properly first. Confirming the diagnosis needs a camera, so it needs an ear, nose and throat surgeon. If you have had eight weeks of a correctly used steroid spray and you still have difficulty breathing through your nose, that is the point to ask for a referral.
Is a deviated septum a health problem or a cosmetic one?
Functional septoplasty is straightforwardly medical care: it is aimed at how you breathe rather than how you look. Straightening a crooked external nose at the same time is a septorhinoplasty, which is a different operation and priced differently. The figures are set out on my pricing page.
If you have suspected this for years and never had it properly looked at, that is worth putting right. You can book a consultation and I will examine your nose with a camera, before and after decongestion, and tell you plainly whether your septum is the problem or whether something else is.
If you would rather talk it through before committing to anything, call us on 020 7183 0220 and we can tell you whether it is worth your while coming in.
Mr David Whitehead is a Consultant ENT and Facial Plastic Surgeon in London, on the GMC Specialist Register for Otolaryngology and certified by the Royal College of Surgeons Intercollegiate Board in Cosmetic Surgery. More about my training and credentials.