Is it better to breathe through your nose or mouth?
At rest and at night, nose breathing is better: your nose warms and humidifies the air, traps dust, and your mouth stays moist. Breathing out through your mouth loses 42 % more water (Svensson, 2006). During exercise, opening your mouth is normal: above about 35 liters of air per minute, most adults breathe through both (Niinimaa, 1981).
Simplified diagram for a healthy adult. Dashed curves are estimates based on published averages.
What does the nose do that the mouth does not?
A head seen in cross-section. Each dot is a bit of air: blue when cold, orange when warm. Through the nose, air passes between warm, moist folds called turbinates and reaches about 34 °C (93 °F) at the back of the nose. Through the mouth, it goes straight in and warms up less. Tap one of the nose's jobs, on the right, to see it on the drawing.
Sources: temperature in the nose, about 34 °C at the back (Keck, Laryngoscope, 2000); the nose warms air 1.5 times better than the mouth (Paczesny, Otolaryngol Pol, 2007); 42 % more water lost through the mouth (Svensson, Rhinology, 2006); switch to the mouth at about 35 L/min (Niinimaa, Respir Physiol, 1981); mouth pH at night (Choi, J Oral Rehabil, 2016); snoring and breathing pauses (Fitzpatrick, Eur Respir J, 2003); 15 times more nitric oxide when humming (Weitzberg and Lundberg, Am J Respir Crit Care Med, 2002). Air temperature through the mouth and the filtering role: estimates with no measured figure here (to be checked).
Keyboard: 1 to 5 for the situation, Space to pause, L for slow motion, Esc clears the selected job.
Frequently asked questions about nose and mouth breathing
Why is it better to breathe through your nose?
Breathing through your nose warms, humidifies and filters the air before it reaches your lungs. By the end of a breath in, the air is already about 34 °C (93 °F) at the back of the nose (Keck, 2000), and the nose warms it about 1.5 times better than the mouth (Paczesny, 2007). When you breathe out, it takes back some of the water: through the mouth, you lose 42 % more (Svensson, 2006). The nose also adds a little nitric oxide made by the sinuses to the air (Lundberg, 1995).
Is it bad to sleep with your mouth open?
Sleeping with your mouth open is not serious in itself, but it dries out your mouth and makes snoring more likely. In 10 volunteers, the mouth was more acidic at night when breathing through the mouth: average pH 6.6 versus 7.0, and at times below 5.5, the level where tooth enamel starts to dissolve (Choi, 2016). In 12 healthy adults, sleeping while breathing through the mouth raised breathing pauses from 1.5 to 43 per hour (Fitzpatrick, 2003). Loud snoring with pauses, or heavy tiredness during the day, is worth discussing with a doctor.
Should you tape your mouth shut to sleep?
Taping your mouth at night is not recommended: the evidence is weak and there is a risk if your nose gets blocked. A 2025 review pooled 10 studies and 213 patients, all of low quality; only 2 showed a small benefit, in people with mild sleep apnea (Rhee et al., PLOS ONE, 2025). The authors warn of a risk of suffocation when the nose is blocked. It is better to look for why you breathe through your mouth: a stuffy nose, allergies, large tonsils.
Should you breathe through your nose or your mouth when running?
When running easy, you can breathe through your nose; as the effort rises, opening your mouth is normal. In 20 out of 30 adults, the mouth opened at about 35 liters of air per minute, and at 90 liters the mouth carried 61 % of the air (Niinimaa, 1981). With the mouth closed, maximal airflow dropped much more than maximal oxygen uptake, but all participants could still train for endurance (Morton, 1995). For a hard effort, the mouth helps.
Why is one nostril always more blocked than the other?
Having one nostril more blocked than the other is normal: it is the nasal cycle, found in about 70 to 80 % of adults (Pendolino, 2018). The blood vessels on each side swell and shrink in turn. In 33 people followed for 24 hours, a cycle lasted about 2 hours awake and 4 h 30 min asleep, and lying on one side opened the upper nostril (Kahana-Zweig, 2016). If one side stays blocked all the time, it is best to see a doctor.
My child breathes through their mouth: should I worry?
A child who often breathes through the mouth, especially at night, is worth mentioning to their doctor. Depending on the study, 11 to 56 % of children breathe through the mouth, most often because of large adenoids, large tonsils or a nasal allergy (Zhang, Front Public Health, 2024). Over time, it is linked to ear infections, sleep apnea, a narrow palate and a longer face. Treating the cause often brings back nose breathing.
True or false?
Cold air reaches your lungs still cold.
False. Whatever the route, air is close to 98.6 °F (37 °C) and saturated with water by the time it reaches deep in the lungs. Through the nose, it already reaches 93 °F (34 °C) at the back of the nasal passages (Elad, 2008; Keck, 2000).
Humming flushes air out of your sinuses.
True. When you hum, the air in the sinuses is renewed much faster: about 15 times more nitric oxide is measured in the nose (Weitzberg and Lundberg, 2002).
Everyone breathes through their nose at rest.
False. Out of 30 adults, 4 breathed through the mouth even at rest, and only 5 always stayed with the nose, even during exercise (Niinimaa, 1981).
This page as text
The same information as the charts, to read without animation: for each chart, the values at the main moments, then the notes with their level of evidence.
When does the mouth take over?
The harder you breathe, the more your nose slows the air down. Past a certain airflow, your mouth opens and the two share the work. Drag along the airflow.
| Airflow, hours of sleep or the path of the air | Share of air through the nose (%) | Share of air through the mouth (%) | Air through the nose (L/min) (dotted) | What happens |
|---|---|---|---|---|
| 0 L/min | 100 | 0 | 0 | (at rest, rough estimate): 100 % through the nose, 0 % through the mouth, so 0 L/min through the nose |
| 20 L/min | 100 | 0 | 20 | (easy walking, rough estimate): 100 % through the nose, 0 % through the mouth, so 20 L/min through the nose |
| 40 L/min | 55 | 45 | 22 | (brisk walking or light jogging, rough estimate): 55 % through the nose, 45 % through the mouth, so 22 L/min through the nose |
| 60 L/min | 46 | 54 | 28 | (running, rough estimate): 46 % through the nose, 54 % through the mouth, so 28 L/min through the nose |
| 80 L/min | 41 | 59 | 33 | (hard effort, rough estimate): 41 % through the nose, 59 % through the mouth, so 33 L/min through the nose |
| 100 L/min | 37 | 63 | 37 | (hard effort, rough estimate): 37 % through the nose, 63 % through the mouth, so 37 L/min through the nose |
Key points
- At rest, the nose is enough (Up to 35 L/min, Shown in humans)
In 20 out of 30 adults, all the air went through the nose up to 35 liters per minute on average, with big differences from one person to the next. At rest, we breathe about 6. Source: Niinimaa, Cole, Mintz and Shephard, « Oronasal distribution of respiratory airflow », Respir Physiol, 1981 - Mouth opens (From 35 to 45.01 L/min, Shown in humans)
Right after the switch, the nose still carries 57 % of the air. At 45 L/min, nose and mouth split it half and half. Source: Niinimaa, Cole, Mintz and Shephard, « Oronasal distribution of respiratory airflow », Respir Physiol, 1981 - All out, the mouth does most of the work (Above 45 L/min, Shown in humans)
At 90 L/min, 61 % of the air goes through the mouth. The nose keeps working: it still carries more than 30 liters per minute. Source: Niinimaa, Cole, Mintz and Shephard, « Oronasal distribution of respiratory airflow », Respir Physiol, 1981 - Not everyone is the same (Throughout, Shown in humans)
Of the 30 adults, 5 always breathed through the nose, 4 through the mouth even at rest, and 1 switched with no pattern. Source: Niinimaa, Cole, Mintz and Shephard, « Oronasal distribution of respiratory airflow », Respir Physiol, 1981 - Nose-only breathing limits maximal effort (Above 55 L/min, Shown in humans)
With the mouth closed, maximal airflow drops much more than maximal oxygen uptake. Yet all participants could still reach an endurance training intensity. Source: Morton et al., « Comparison of maximal oxygen consumption with oral and nasal breathing », Aust J Sci Med Sport, 1995
Mouth open at night: the mouth becomes more acidic
When you sleep with your mouth open, saliva dries up and your mouth becomes more acidic. The curve shows pH, from 3 (very acidic) at the bottom to 8 at the top.
| Airflow, hours of sleep or the path of the air | Mouth pH, mouth closed (dotted) | Mouth pH, mouth open (dotted) | Threshold where enamel dissolves (pH 5.5) | What happens |
|---|---|---|---|---|
| Bedtime | 86 | 86 | 50 | At bedtime: mouth pH about 7.3 with the mouth closed, 7.3 with the mouth open (estimated shape); tooth enamel starts to dissolve below 5.5 |
| 2 h | 81 | 75 | 50 | After 2:00: mouth pH about 7.0 with the mouth closed, 6.8 with the mouth open (estimated shape); tooth enamel starts to dissolve below 5.5 |
| 4 h | 78 | 70 | 50 | After 4:00: mouth pH about 6.9 with the mouth closed, 6.5 with the mouth open (estimated shape); tooth enamel starts to dissolve below 5.5 |
| 6 h | 76 | 67 | 50 | After 6:00: mouth pH about 6.8 with the mouth closed, 6.3 with the mouth open (estimated shape); tooth enamel starts to dissolve below 5.5 |
| 8 h | 76 | 66 | 50 | After 8:00: mouth pH about 6.8 with the mouth closed, 6.3 with the mouth open (estimated shape); tooth enamel starts to dissolve below 5.5 |
Key points
- 6.6 instead of 7.0 (All night, Shown in humans)
In 10 volunteers, average mouth pH during sleep was 6.6 when breathing through the mouth, versus 7.0 when breathing through the nose, and 7.3 during the day. Source: Choi et al., « Intraoral pH and temperature during sleep with and without mouth breathing », J Oral Rehabil, 2016 - At times, below the enamel threshold (After 3 h, Shown in humans)
With the mouth open, pH dropped at times as low as 3.6. Tooth enamel starts to dissolve below 5.5. Mouth temperature, on the other hand, did not change. Source: Choi et al., « Intraoral pH and temperature during sleep with and without mouth breathing », J Oral Rehabil, 2016 - A blocked nose leads to snoring (All night, Shown in humans)
In 12 healthy adults, sleeping while breathing through the mouth (nose blocked) multiplied throat resistance by 2.4 and raised breathing pauses from 1.5 to 43 per hour. Source: Fitzpatrick et al., « Effect of nasal or oral breathing route on upper airway resistance during sleep », Eur Respir J, 2003 - The shape of the curves is estimated (All night, Hypothesis)
The study gives averages over the night. The gradual drop drawn here is an estimate.
The nose warms air better than the mouth
Incoming air is warmed and humidified along the way. The nose, with its folds, does it better and sooner. Drag from the entrance to the bronchi, in a room at 72 °F (22 °C).
| Airflow, hours of sleep or the path of the air | Air breathed in through the nose (°C) | Air breathed in through the mouth (°C, estimate) (dotted) | What happens |
|---|---|---|---|
| 0 cm | 12 | 12 | 0.0 cm at the entrance (nostrils or lips): air at 22.0 °C through the nose, 22.0 °C through the mouth (estimate) |
| 5 cm | 65 | 28 | 5.0 cm between the turbinates of the nose: air at 31.0 °C through the nose, 24.8 °C through the mouth (estimate) |
| 10 cm | 82 | 59 | 10.0 cm in the back of the nose: air at 34.0 °C through the nose, 30.0 °C through the mouth (estimate) |
| 15 cm | 88 | 71 | 15.0 cm in the throat: air at 35.0 °C through the nose, 32.0 °C through the mouth (estimate) |
| 20 cm | 94 | 82 | 20.0 cm in the windpipe: air at 35.9 °C through the nose, 34.0 °C through the mouth (estimate) |
| 25 cm | 97 | 92 | 25.0 cm in the bronchi: air at 36.6 °C through the nose, 35.6 °C through the mouth (estimate) |
| 30 cm | 100 | 100 | 30.0 cm in the bronchi: air at 37.0 °C through the nose, 37.0 °C through the mouth (estimate) |
Key points
- The nasal valve warms the most (Up to 5.01 cm, Shown in humans)
Measured in 50 volunteers: temperature rises mostly in the first few centimeters, at the valve, the narrowest passage of the nose. Source: Keck, Leiacker, Riechelmann and Rettinger, « Temperature profile in the nasal cavity », Laryngoscope, 2000 - About 34 °C (93 °F) in the back of the nose (From 8 to 12.01 cm, Shown in humans)
At the end of breathing in, air reaches about 34 °C (93 °F) at the back of the nose, even before the throat. Source: Keck, Leiacker, Riechelmann and Rettinger, « Temperature profile in the nasal cavity », Laryngoscope, 2000 - 1.5 times better than the mouth (From 5 to 18.01 cm, Shown in humans)
In 30 adults at 72 °F (22 °C), the nose warmed inhaled air about 1.5 times better than the mouth, and recovered about 3 times more heat from exhaled air. Source: Paczesny et al., « Air temperature measurements in nasal cavities and oral cavity », Otolaryngol Pol, 2007 - 42 % more water lost (Beyond 0 cm, Shown in humans)
Breathing out through the mouth loses 42 % more water than through the nose (19 volunteers at rest): the nose takes back some of the moisture on the way out. Source: Svensson et al., « Increased net water loss by oral compared to nasal expiration in healthy subjects », Rhinology, 2006 - 37 °C (98.6 °F) and saturated air deep inside (Beyond 18 cm, Shown in humans)
Whatever the route, air reaches the lungs at almost 37 °C (98.6 °F) and saturated with water. The nose does the biggest share of the work; the throat and windpipe finish the job. Source: Elad, Wolf and Keck, « Air-conditioning in the human nasal cavity », Respir Physiol Neurobiol, 2008
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