Mouth breathing while sleeping: signs, causes and how to stop

Short answer

Mouth breathing while sleeping means that for part of the night, air bypasses your nose. It usually happens because the nose is blocked or because the jaw drops open as you relax into sleep. The most common signs are a dry mouth, a sore throat or snoring. To stop it, first find out how much of the night it actually happens, then deal with the cause: a congested nose, your sleeping position, or habit.

Signs you breathe through your mouth at night

You are asleep when it happens, so you never see it directly. What you notice is the aftermath. The most common signs of mouth breathing during sleep are:

Waking up with a dry mouth or reaching for water during the night
A sore or scratchy throat in the morning that fades during the day
Snoring, usually reported by whoever sleeps next to you
Bad breath on waking
Dry or chapped lips, or drool on the pillow
Waking up tired even after a full night in bed

None of these prove it on their own. A dry mouth can come from a dry bedroom, and tiredness has a hundred causes. The only way to know how much of the night you breathe through your mouth is to measure it.

Why mouth breathing happens during sleep

Breathing defaults to whichever route has the least resistance. When the nose is harder to breathe through, the mouth takes over, and during sleep nothing stops it. Common reasons:

A blocked nose. Colds, allergies and chronic rhinitis all swell the lining of the nose.
The structure of the nose. A deviated septum or enlarged turbinates narrow the airway. In children, enlarged adenoids or tonsils are a frequent cause.
Sleeping on your back. The jaw falls open more easily, and the mouth becomes the easier path.
Alcohol and sedatives. They relax the muscles that keep the mouth closed and the airway open.
Habit. People who breathe through their mouth during the day tend to keep doing it at night.

What mouth breathing does to your sleep

Your nose is built for breathing. It filters, warms and humidifies the air, and its narrow passages add a little resistance that slows each breath down. The sinuses also release nitric oxide into the air you breathe in. Mouth breathing skips all of this.

Breathing through the mouth at night is linked to a dry mouth, snoring and more fragmented sleep. That is why you can spend eight hours in bed, get a good sleep score from your watch and still wake up feeling like you didn't sleep. Read more about the benefits of nasal breathing.

How to stop mouth breathing at night

Measure it first. Know how many hours of the night you breathe through your mouth, and when. Without a baseline you can't tell whether anything you try works.
Clear your nose. Saline rinses before bed, treating allergies and keeping the bedroom air from getting too dry all make nasal breathing easier. If your nose is blocked most of the time, see a doctor.
Sleep on your side. Side sleeping keeps the jaw from falling open and often reduces snoring as well. See snoring and sleep position.
Try a nasal strip or dilator. They hold the nostrils open mechanically and make the nose the easier route.
Skip alcohol late in the evening. It relaxes the muscles that keep your mouth closed.
Practise nose breathing during the day. Daytime habits carry into the night. Myofunctional therapy can help with this.
Be careful with mouth tape. The evidence for it is thin, and it is unsafe if your nose is blocked. See does mouth taping work?

When to talk to a doctor

Loud snoring with gasping or pauses in breathing, heavy daytime sleepiness or morning headaches can be signs of obstructive sleep apnea. Talk to a doctor. The same goes for a nose that is blocked most of the time, and for a child who breathes through their mouth at night.

How FLOU measures mouth breathing

FLOU is a small sensor worn across the bridge of the nose. It measures the airflow at your nose all night and tells you, breath by breath, whether you were breathing through your nose or your mouth. In the morning you see your nose vs. mouth breathing ratio, when the mouth breathing happened, and which position you were lying in at the time. You can then try a change, such as side sleeping, a nasal strip or a saline rinse, and see whether the number moves.

Frequently asked questions

Is mouth breathing while sleeping bad?

Occasional mouth breathing is normal, for example during a cold. Regular mouth breathing at night is linked to a dry mouth, snoring and poorer sleep quality, so it is worth finding out how often it happens and why.

How do I know if I breathe through my mouth while sleeping?

Common signs are waking with a dry mouth or sore throat, snoring and morning tiredness. These are indirect, though. To know how much of the night you breathe through your mouth, you need to measure airflow at the nose during sleep, which is what FLOU does.

Can you stop mouth breathing at night on your own?

Often, yes. Clearing a congested nose, sleeping on your side, using a nasal strip and avoiding alcohol before bed all help. If your nose is blocked most of the time, a doctor can check for structural causes such as a deviated septum.

Does mouth breathing cause snoring?

Mouth breathing makes snoring more likely, because an open mouth lets the jaw and tongue fall back and narrow the airway. Many people snore less once they breathe through their nose.

FLOU is a wellness device. It is not intended to diagnose, treat, cure or prevent any disease. This guide is general information, not medical advice. Talk to a clinician about sleep-disordered breathing.