When your nose suddenly stops breathing well, the cause is usually one of two things: a virus (a cold) or a flare-up of allergies. The clues below can help you tell them apart, which makes it easier to know what to expect and how to treat it. 

Clues that point to a virus 

If you have been around small children or people who are sick, a virus is the most likely cause. Colds don't all feel the same — there are hundreds of different cold viruses, and each one can act a little differently. 

Colds often start in one spot — one side of the nose, the throat, or the chest — and over a day or two spread to the rest of the upper airway. People often make a lot of clear, runny mucus at first. 

When you aren't sure, it is safest to treat sudden nose blockage as if it is a cold. Assume you can spread it, and wash your hands often.

If allergies might also be involved, I usually still treat it as a cold but add an antihistamine (an allergy medicine) to the plan.

Clues that point to allergies or nose irritation

If you have just been around something you are allergic to, an allergy flare-up is possible. A short-term reaction to an irritant (called non-allergic rhinitis — irritation of the nose lining without a true allergy) can do the same thing. Both usually settle down quickly once you get away from whatever caused it.

Common nose irritants 
Perfumes, solvent fumes, smoke, dust 

Allergies and nose irritation usually come with a history of similar short episodes in the past. Sneezing, itchy red eyes, no sore throat, and no cough are all clues that one of these is to blame. If sudden blockage doesn't happen to you often, and you haven't been around any obvious irritant, then allergies probably aren't the reason.

When the nose feels blocked often, several causes are common: long-lasting sinus infection (chronic sinusitis), year-round allergies, enlarged turbinates (the scroll-shaped structures inside the nose that can swell up), and the natural shape of the inside of the nose.

It can be hard to know which one is the problem from the blockage alone. An exam is usually what narrows it down.

If you also have sinus pain or headaches, this points to a long-lasting infection.
If you also have sneezing, itchy eyes, and flare-ups by season, allergies are likely.
If you have asthma or react to aspirin, growths in the nose lining (nasal polyps) are more likely.
If you have ever had a nose injury, a crooked wall inside the nose (deviated septum) is possible.


You can start with the steps in the over-the-counter section for long-lasting nose problems. If things don't improve, see a specialist.

When only one side is blocked, a few causes become much less likely. For example, allergies rarely affect only one side. A crooked wall inside the nose (deviated septum) is a more likely cause when blockage is mostly on one side.

Long-lasting infections and growths in the nose lining (nasal polyps) can also show up on only one side — in fact, they often do. With one-sided blockage, an exam by a specialist will usually find the cause. The over-the-counter steps for long-lasting nose problems are a reasonable place to start. 

Trouble breathing when you lie down is a very common complaint. The usual story is that as soon as you lie down, your nose stuffs up. Often the side that is "downhill" feels worse, and if you roll over, the sides swap — one opens up and the other closes off.

Here is why: the scroll-shaped structures inside the nose (turbinates) are the parts that can change size the most. They are full of blood vessels that can swell or shrink. When you are up and about, your head is "propped up" all day. When you lie down and your head is at the same level as your heart, blood pools more easily and the vessels can swell. Even the small height difference between the upper and lower sides when you lie on your side can make a difference.

For some people, this is layered on top of other nose problems and is the only time those problems cause trouble.

Another possible reason for nighttime nose blockage is being allergic to dust mites — tiny bugs that live in bedding. This has nothing to do with how clean your house is. If you think this might be the cause, you can buy special mattress and pillow covers that keep the dust mites trapped away from your face. You can't get rid of dust mites entirely, so blocking them is the answer.

I usually suggest a steroid nose spray before bed. It can help with either cause. Try it for at least a week before deciding if it works. If it doesn't help and the problem has been going on a long time, see a specialist. Sometimes a simple in-office procedure that shrinks the turbinates from underneath the lining (a turbinate reduction) can fix this and improve sleep. Breathing through the nose better can also help some snorers.

Blockage that flares up by season is most often from allergies — pollens, molds, or other things in the air at certain times of year. The usual treatments are the over-the-counter ones for long-lasting nose problems: saltwater rinses, steroid nose sprays, and allergy pills (antihistamines). If the problem is severe or doesn't get better with these, a specialist can help with allergy testing or stronger treatments.