Nose breathing vs mouth breathing: what the nose actually does

Almost every exercise on this site says to breathe in through the nose. It is such a standard instruction that it usually goes unexplained, which is a shame, because the reason is concrete and it tells you when the instruction stops mattering.

What the nose does that the mouth does not

Roughly twelve thousand litres of air pass through an adult nose every day, and it is hydrated and filtered on the way through. The nose exists in large part to protect the airways below it from gases, particles and pathogens — the mouth does none of that (GMS Current Topics in Otorhinolaryngology).

The nose and the sinuses also produce nitric oxide, which has a regulating role in the airways below. This is the fact most often stretched online. It is real physiology, and it is a long way from the claims built on top of it.

There is a practical point too. The nose is a narrower passage than the mouth, and it cannot pass as much air — which is why nasal breathing stops being workable once you are working hard and need more of it. For a breathing exercise, where the whole point is a small, quiet breath, that limit is not in your way.

What is known about habitual mouth breathing

Most of the research here is about children, and about mouth breathing that is caused by something — a blocked nose, enlarged adenoids or tonsils. In that context it is common, with reported prevalence between 11 and 56 percent, and reviews associate it with altered dental and facial development and with a higher risk of caries and gum disease (Frontiers in Public Health).

Two things are worth holding onto. The usual cause is an obstruction rather than a habit, which means the useful question is why the nose is blocked. And findings in children who breathe through their mouths all night are not findings about an adult who opens their mouth on a hard hill.

Mouth taping, honestly

If you searched for this, you have probably met mouth taping. A systematic review looked specifically at whether the trend holds up: ten studies met its criteria, covering 213 patients in total. Two showed a statistically significant improvement in sleep-apnoea markers. The others showed no difference, and the review raised the risk of asphyxiation where a nose is obstructed. Notably, many of the studies excluded anyone with nasal obstruction in the first place (PLOS One systematic review).

That is a thin evidence base carrying a lot of confident advice. The group most drawn to taping — people who breathe through their mouths at night because their nose does not work well — is the group the review flags as most at risk and the group most of the studies left out.

• If you breathe through your mouth at night, the thing to investigate is why your nose is blocked, with someone qualified to look.
• Taping your mouth shut does not fix an obstruction; it removes the way around one.
• Persistent snoring, waking unrefreshed, or daytime sleepiness are reasons to see a clinician rather than to buy tape.

So what should you actually do

Breathe in through your nose during breathing exercises, because it is quieter, slower and gentler, and because the nose is doing work the mouth cannot. Let your mouth open when you are exerting yourself and need the air — that is the mouth doing its job, not a failure. And if your nose is blocked often enough that you cannot use it, treat that as the thing to look into, rather than as something to breathe around.

Slow breathing - The pace that does most of the work, whichever route the air takes.

Hyperventilation and overbreathing - What happens when you breathe more than your body needs, and how to settle it.

The Buteyko method - A named method built around nasal, reduced breathing — and what the evidence says about it.