Nasal vs Mouth Breathing: What the Research Actually Says

A few years ago, James Nestor's book Breath turned nasal breathing into a wellness conversation. The book argued that modern humans have largely forgotten how to breathe properly, that we breathe through our mouths far too often, and that switching to nasal breathing transforms health in ways most doctors do not appreciate.

Some of that is true. Some of it is overstated. And there is a real, careful body of research underneath the popularisation that is worth knowing on its own terms, without the marketing.

If you want to start training your nose right away, the Alternate Nostril Breathing tool is a traditional pranayama practice that strengthens nasal awareness.

The basic physiology

Your nose does several things to incoming air that your mouth does not.

It filters. The nasal hairs trap particulates and the mucus catches small irritants before they reach the lungs. The mouth has none of this.

It warms and humidifies. By the time air reaches the back of your throat through the nose, it is close to body temperature and saturated with moisture. Cold dry air through the mouth reaches the lungs cold and dry, which is harder on bronchial tissue and contributes to exercise-induced bronchoconstriction in cold weather.

It resists. The nasal passages are narrower than the mouth. Breathing through the nose takes slightly more effort, which trains the respiratory muscles and slows the breath. Most people breathe noticeably faster through the mouth than through the nose, even at rest.

It produces nitric oxide. This is the piece Nestor's book emphasised, and the science is real. The paranasal sinuses produce nitric oxide (NO), a gas that has vasodilatory effects on the lung's blood vessels. When you breathe in through your nose, you carry some of that nitric oxide into the lungs, where it appears to improve oxygen uptake efficiency. Lundberg and colleagues' 1997 paper in Nature Medicine and the work that followed established this clearly. Estimates suggest nasal breathing may improve oxygen absorption by roughly 10 to 20 percent compared to mouth breathing, though the size of this effect is debated.

What changes when you breathe through your nose

For most people, switching from habitual mouth breathing to nasal breathing produces several measurable changes within weeks.

Slower breath rate. People typically drop from 14 to 20 breaths per minute through the mouth to 10 to 14 through the nose. The slower rate is calming for the nervous system on its own, before any other effects.

More efficient exercise. This is the surprising one. A 2017 study by Recinto and colleagues found that endurance athletes who switched to nasal breathing during training experienced no decrease in performance after an adaptation period, despite the higher resistance. Some athletes report improved endurance, likely from the slower breath rate and better CO2 tolerance.

Better humidification of the airways. Less dry mouth, less throat irritation in cold weather.

Improved sleep quality for some people. Mouth breathers often snore more, wake up with dry mouth, and report worse sleep quality. Switching to nasal breathing during sleep (often using a small piece of tape over the lips, controversially) can help. More on this below.

Slightly reduced anxiety symptoms. The slower, more controlled nasal breath tends to activate parasympathetic tone, which calms the system.

The mouth-breathing problem

Chronic mouth breathing is more than a quirk of preference. In children especially, sustained mouth breathing during sleep and development has been associated with several real concerns.

Lee and colleagues' 2015 review in Sleep and Breathing documented connections between habitual mouth breathing in children and altered facial development (longer face, flatter cheekbones, narrower dental arch), orthodontic problems, and increased risk of sleep-disordered breathing. The mechanism is thought to be that an open-mouth posture changes the resting position of the tongue, which influences how the upper jaw develops.

In adults, the concerns are less developmental but still meaningful. Habitual mouth breathing is associated with dry mouth, increased risk of dental cavities and gum disease (saliva protects teeth, and mouth breathing reduces saliva), worse sleep quality, and in some cases higher snoring rates.

If you find yourself breathing through your mouth most of the time, especially during sleep, it is worth asking why. The two common causes are nasal obstruction (allergies, deviated septum, large turbinates) and habit. Obstruction is medical; talk to an ENT. Habit can be retrained.

What about mouth taping during sleep?

This is the Nestor book's most viral recommendation. A small piece of tape across the lips at bedtime forces nasal breathing. Reports from users are enthusiastic. The published evidence is thin.

There are a small number of recent trials and a lot of case reports. Most suggest it helps people who snore primarily due to habitual mouth breathing rather than significant airway obstruction. Improvements in sleep quality and snoring volume are common. The downside risks are minimal for healthy adults, though it is uncomfortable for some people initially.

The serious caution: if you have sleep apnea (especially undiagnosed), forcing nasal breathing with tape can be dangerous if your nose is not actually capable of supporting your breathing. People with significant nasal obstruction will compensate during apnea events with mouth breathing; remove that compensation and you may worsen the apnea.

Before trying mouth taping, you should be able to comfortably breathe through both nostrils for a few minutes during the day. If you cannot, address the obstruction first. If you have any symptoms of sleep apnea (loud snoring, witnessed pauses in breathing, daytime fatigue), get a sleep study before experimenting.

A reasonable starting protocol if you are healthy and want to try it: use a small piece of porous medical tape (like 3M's Micropore) across the centre of your lips, not sealing the corners. This makes it easy to break open if you need to. Start with naps before overnight.

How to retrain habitual mouth breathing

If you breathe through your mouth most of the day, your nasal passages have been underused, and breathing through your nose feels effortful at first. This is reversible.

1. Notice. For three days, periodically check whether your mouth is open or closed when you are not speaking. Do not change anything yet. Just notice.

2. Close your mouth at rest. Once you have noticed, start consciously keeping your mouth closed when you are not speaking, eating, or actively exerting. This sounds trivial. It is the whole intervention.

3. Practice slow nasal breathing during low-effort tasks. Walking, washing dishes, sitting on the train. Five-second inhale, five-second exhale through the nose. This is essentially coherent breathing.

4. Use the nose during light exercise. Walking, easy cycling, slow jogging. Push hard exercise through nasal breathing only later, once it feels comfortable at lower intensities.

5. Address obstructions. Persistent congestion, allergies, or chronic mouth breathing despite effort warrants a doctor visit.

The transition takes a few weeks for most adults. The nose has to clear, the diaphragm gets stronger, and the brain has to relearn that nasal breathing is the default.

Where the claims overshoot

A few claims in the popular nasal-breathing literature do not have strong scientific support.

The idea that nasal breathing "rewires" the brain to a fundamentally calmer baseline within weeks is overstated. Nasal breathing during a session is calming. The long-term trait effects of having switched to nasal breathing exist but are modest.

The idea that mouth breathing is responsible for most modern face shapes or that switching can re-sculpt an adult face is implausible. Childhood developmental effects are well-documented. Adult facial bones do not reshape.

The idea that all athletic performance is improved by nasal-only breathing during exercise is mixed in the data. For low to moderate intensity, nasal breathing is fine and probably beneficial. For high-intensity work, mouth breathing is necessary for sufficient air exchange, and forcing nasal-only at maximum effort harms performance.

The healthy summary: nasal breathing is the right default. It is worth retraining if you have drifted toward habitual mouth breathing. It is not a panacea.

FAQ

For other breath practices to try alongside nasal retraining, the breathing hub lists them by purpose. If you want to layer a meditation on top, our Meditation Timer works well after a few minutes of slow nasal breathing.