Mouth breathing versus nose breathing in sleep: in 12 healthy volunteers, upper airway resistance was higher and the apnea-hypopnea index far higher (43 against 1.5) when they breathed through the mouth, which is why the nose is the default route. Mouth breathing goes with a dry mouth, a lower mouth pH and, in children, changes in facial growth, but it is more often a sign of a blocked nose or of sleep apnea than a habit, and claims about extra oxygen or better workouts did not hold in the small trials.
Mouth breathing versus nose breathing has become a social media argument, with big claims on both sides: the nose is said to filter, warm and boost, and the mouth is said to ruin sleep, teeth and faces. Some of it has data behind it. Some of it has a single small trial or a computer simulation. This page sorts the two.
It covers what happens to the airway in sleep, what mouth breathing does to the mouth and to children, which nasal breathing claims held up, and what a systematic review found about mouth taping. It is information, not advice to change how you breathe, and a blocked nose or loud snoring is a reason to ask a doctor.
Mouth breathing v nose breathing: the comparison in one table
The table lines up the comparisons that have actual studies behind them, with the size of the study.
| Topic | Nose | Mouth | Study behind it |
|---|---|---|---|
| Airway resistance in sleep | Median 5.2 cmH2O/L/s | Median 12.4 cmH2O/L/s | 12 healthy volunteers, crossover |
| Obstructive events in sleep | Apnea-hypopnea index 1.5 | Apnea-hypopnea index 43 | Same 12 volunteers |
| Mouth acidity in sleep | Mean pH 7.0 | Mean pH 6.6 | 10 healthy adults, nose clip |
| Air conditioning | About 90% of the heat and water needed | Not modelled | Computer simulation of nasal airflow |
| Power in all-out cycling | Same | Same | 49 healthy adults |
| Blood oxygen at rest | Unchanged | Unchanged | 10 patients after heart surgery |
What mouth breathing does to the airway in sleep
The strongest data are mechanical. In a randomized single-blind crossover study, 12 healthy volunteers with normal nasal resistance (aged 30, BMI 23) slept in a nasal breathing and an oral breathing condition. Awake, resistance was similar by both routes. Asleep (supine, stage 2), upper airway resistance was much higher through the mouth (median 12.4 against 5.2 cmH2O per litre per second), and obstructive but not central apneas and hypopneas were far more frequent: an apnea-hypopnea index of 43 with the mouth and 1.5 with the nose. The authors suggest this mechanical advantage may explain why healthy people breathe almost entirely through the nose in sleep.
Fitzpatrick MF, McLean H, Urton AM, et al. Effect of nasal or oral breathing route on upper airway resistance during sleep. Eur Respir J 2003. PMID 14621092
Imaging fits that picture. In 52 patients with obstructive sleep apnea, a 3-D CT scan with the mouth closed and then open showed that opening the mouth narrowed the airway behind the palate and the tongue and lengthened it, at every severity, although total airway volume did not change. The authors read this as a more elongated, narrower airway that may collapse more easily.
Kim EJ, Choi JH, Kim KW, et al. The impacts of open-mouth breathing on upper airway space in obstructive sleep apnea: 3-D MDCT analysis. Eur Arch Otorhinolaryngol 2011. PMID 20957487
The direction of cause is not settled, though. In 41 snorers with normal nasal resistance, the 28 with sleep apnea spent more of the night breathing through the mouth or mouth and nose together than the 13 simple snorers, and the apnea-hypopnea index was the main factor explaining how much. So mouth breathing may be a cause of worse breathing in sleep, and it may also be a result of it.
Koutsourelakis I, Vagiakis E, Roussos C, et al. Obstructive sleep apnoea and oral breathing in patients free of nasal obstruction. Eur Respir J 2006. PMID 17005578
Is mouth breathing bad for you? Teeth, dry mouth and children
For the mouth itself there is some evidence. Ten healthy adults slept two nights each wearing a custom appliance with a pH probe and a thermocouple, once normally and once with a nose clip to simulate mouth breathing. Mean intraoral pH during normal sleep was 7.0 (SD 0.5) and 6.6 (SD 0.5) with the nose clipped, a significant drop that the authors note has been proposed as a causal factor for tooth erosion and decay. It is a tiny study with an artificial blockade, so it shows a mechanism and not the real-life size of the risk. A dry mouth and bad breath on waking are the everyday signs, covered in Dry mouth every morning and Morning breath.
Choi JE, Waddell JN, Lyons KM, et al. Intraoral pH and temperature during sleep with and without mouth breathing. J Oral Rehabil 2016. PMID 26666708
In children the stakes differ, because bones are still growing. A systematic review and meta-analysis of 10 studies in children found that mouth breathing went with backward and downward rotation of the upper and lower jaw, a steeper bite plane, and airway narrowing that was common in the mouth breathers. Children with a persistently open mouth, snoring or restless sleep should be assessed, since the usual cause is something that blocks the nose. The longer story is in Mouth breathing and your face.
Zhao Z, Zheng L, Huang X, et al. Effects of mouth breathing on facial skeletal development in children: a systematic review and meta-analysis. BMC Oral Health 2021. PMID 33691678
Nasal breathing vs mouth breathing: which claims held up
Three claims travel together online. The first is that the nose conditions air. A computer simulation of airflow through anatomical models found that a healthy nose can provide about 90% of the heat and water needed to bring inhaled air near to alveolar conditions, and the replica of a real nose reached 92% of the heating and 96% of the moisture. That is a model, not a measurement in people, but it matches the textbook role of the nose.
Naftali S, Rosenfeld M, Wolf M, et al. The air-conditioning capacity of the human nose. Ann Biomed Eng 2005. PMID 15909660
The second is that nasal breathing raises oxygen through nitric oxide made in the sinuses. A randomized crossover study in 10 patients (mean age 65) on the first day after heart surgery found that nasal breathing lowered pulmonary vascular resistance (256 against 287 dyn s cm-5 cm-2), which fits a nitric oxide effect, but arterial oxygen, carbon dioxide and pH did not change. So the oxygen boost, as such, was not seen.
Settergren G, Angdin M, Astudillo R, et al. Decreased pulmonary vascular resistance during nasal breathing: modulation by endogenous nitric oxide from the paranasal sinuses. Acta Physiol Scand 1998. PMID 9715735
The third is that nasal breathing improves performance. Forty-nine healthy adults did two all-out cycling tests, one breathing through the nose and one through the mouth. Power output did not differ (peak around 730 to 750 W, p = 0.2), and muscle desaturation was the same. Effort felt higher with the mouth (Borg 9.0 against 8.0, p = 0.04), and muscle oxygen recovered faster and further afterwards with the nose (0.45 against 0.23 percent per second). The authors suggest the nitrate-nitrite-nitric oxide pathway as an explanation, but this is a single study of short efforts.
Lévénez M, Lévêque C, Lafère C, et al. Effect of Oral Versus Nasal Breathing on Muscular Performance, Muscle Oxygenation, and Post-Exercise Recovery. Sports (Basel) 2025. PMID 41150503
The summary: the nose protects the airway in sleep and conditions air, and the extra-oxygen and better-workout claims are not supported by what has been measured.
Nose vs mouth breathing and snoring
Snoring sits between the two routes. In 4,916 adults of the Wisconsin Sleep Cohort, severe night-time nasal congestion had an odds ratio of 3.0 (95% confidence interval 2.2 to 4.0) for habitual snoring compared with no congestion, and the link held among people without frank sleep apnea. It is a survey, so it shows that a blocked nose and snoring go together, not that clearing the nose stops the snoring. Combined with the airway findings above, it explains why a blocked nose is the first thing doctors look at when snoring and mouth breathing show up together. What causes snoring? and Do nasal strips work for snoring? go into the rest.
Young T, Finn L, Palta M. Chronic nasal congestion at night is a risk factor for snoring in a population-based cohort study. Arch Intern Med 2001. PMID 11427099
What these studies do not tell you
Most of the work above forces one route for a night, in groups of 10 to 50 people, and measures something that can be measured in a night. None of it followed habitual mouth breathers for years, and none shows that retraining your breathing route changes health outcomes in adults. The study in children is a pooled look at observational work, which cannot separate cause from effect: a child with enlarged adenoids breathes through the mouth and may also have a narrow jaw for other reasons. Read the numbers as a map of mechanisms, not as a forecast for you.
Why people breathe through the mouth, and what taping adds
Most mouth breathing has a reason. A blocked nose (allergy, a cold, a crooked septum), sleep apnea, and enlarged tonsils or adenoids in children are the common ones. If the nose is the bottleneck, Can a deviated septum cause snoring? and How to stop mouth breathing go through what is known.
Mouth taping is the social media answer, and a systematic review has looked at it. Ten studies with 213 patients met the inclusion criteria. Two showed a significant improvement in markers of sleep apnea such as the apnea-hypopnea index or oxygen desaturations; the others found no difference, and some discussed potential risks, including asphyxiation when the nose is blocked. Many studies had excluded people with nasal obstruction. The reviewers concluded that there is potentially serious risk of harm in indiscriminate use and that benefit needs further study. The longer version is in Does mouth taping work?.
Rhee J, Iansavitchene A, Mannala S, et al. Breaking social media fads and uncovering the safety and efficacy of mouth taping in patients with mouth breathing, sleep disordered breathing, or obstructive sleep apnea: A systematic review. PLoS One 2025. PMID 40397877
When to see a doctor
See a doctor if your nose is blocked most of the time and sprays or rinses do nothing, if you snore loudly and a partner sees you stop breathing, if you are sleepy through the day, or if your child breathes through an open mouth, snores or sleeps restlessly. These are usually fixable causes, and they are a better target than the breathing route itself.
What SleepTrace can and cannot tell you about mouth breathing
SleepTrace does not detect mouth breathing, dry mouth or the route your air takes. It listens through the microphone of your phone, labels snoring, talking and coughing and keeps playable clips of them (3 a month on the free plan), and marks apparent breathing pauses with a timestamp, not a clip. For this topic the useful part is the snoring: whether it comes in long stretches or short bursts, and at what hour, which you can bring to an appointment. The app runs on iPhone and Android; keep it open (the screen dims by itself) and the phone on its charger. Phases are estimates, and the sleep apnea indicator is a screening estimate, not a diagnosis.
Frequently asked questions
The nose, in the experiments. In 12 healthy volunteers with normal nasal resistance, upper airway resistance during sleep was higher when breathing through the mouth (median 12.4 against 5.2 cmH2O per litre per second) and the apnea-hypopnea index was 43 with the mouth against 1.5 with the nose. That was an experiment that forced the route, so it shows the mechanics, not what happens to people who breathe through the mouth by habit.
It can go with problems, but it depends on who and why. In 10 healthy adults, simulated mouth breathing during sleep lowered the mean mouth pH from 7.0 to 6.6, which has been proposed as a factor in tooth erosion and decay. In children, a meta-analysis of 10 studies linked mouth breathing to backward and downward rotation of the jaws. In adults, mouth breathing is more often a sign of a blocked nose or of sleep apnea.
In 49 healthy adults, power output on two all-out cycling tests did not differ between nasal and oral breathing, though effort felt higher with the mouth (Borg 9.0 against 8.0) and muscle oxygen recovered faster afterwards with the nose. It is one small trial of short efforts, so it does not settle the question for training.
It has not been shown. A systematic review of 10 studies with 213 patients found two with a significant improvement in markers of sleep apnea, others with no difference, and a possible risk, including asphyxiation, if the nose is blocked. Many of the studies excluded people with nasal obstruction. The review concluded that indiscriminate taping may carry a serious risk of harm.
No. The app listens through the phone microphone and labels snoring, talking and coughing, with playable clips for each. It cannot tell whether the air went through the nose or the mouth.
SleepTrace is a wellness app, not a medical device. This article is general information, not medical advice. If your symptoms are frequent, severe or worrying, please talk to a doctor.
The studies compare mouth and nose breathing in sleep, but what you want to know is how your own nights look. SleepTrace does not detect mouth breathing. It records sound, marks snoring with a clip, the time and a decibel peak, and shows possible breathing pauses with a time, which gives a doctor something concrete if your nose is blocked or the snoring is loud.
Hear your own night. SleepTrace turns a night of audio into your sleep phases, the sounds you made, and how it all trends. Works without a wearable, better with one. Your phone on the nightstand is enough to start. Get it for iPhone or Android →