Your nose is not a backup airway. Here is what it does that the mouth cannot, what changes when you switch during exercise, and why the mouth-taping trend needs a serious caveat.
Most people breathe through their mouth more than they realise, especially under stress and during exercise. The nose is not simply a narrower version of the same tube. It does several jobs the mouth cannot do at all.
What the nose actually does
Four things, roughly. It filters particles through mucus and cilia. It humidifies and warms incoming air toward body temperature before it reaches the lungs. It creates resistance, roughly double that of mouth breathing, which slows the breath and encourages fuller use of the diaphragm. And it adds nitric oxide to the air you inhale.
The nitric oxide part
This is the piece most people have not heard. The paranasal sinuses continuously produce nitric oxide, a signalling molecule that relaxes smooth muscle and widens blood vessels. Work by Lundberg, Weitzberg and colleagues in the 1990s established that nasal airways are a major source of it and that breathing through the nose carries that nitric oxide down into the lungs, where it appears to improve the matching of blood flow to ventilation. Breathe through your mouth and you bypass the supply entirely.
Breathe through your mouth and you bypass the supply entirely.
Worth keeping this in proportion. It is a genuine and well-documented physiological difference. It is not a performance cheat code, and the studies do not show dramatic changes in outcomes that matter to most people.
Nasal breathing during exercise
Switching to nose-only breathing during training is uncomfortable at first and forces you to slow down, which is exactly why some coaches like it as a pacing tool for easy sessions. Dallam and colleagues ran a small study in 2018 in which recreational runners spent an extended period training with nasal-only breathing and were then tested. Their ventilation rate dropped substantially at a given workload while VO2max was essentially unchanged.
Read that carefully, because it cuts both ways. It means the body adapted efficiently to a restricted airway. It does not mean nasal breathing made them faster. As a practical matter, it is a good self-limiting governor for zone 2 work, where the whole point is staying easy. At high intensity your body will open the mouth, and it should.
Sleep and the daytime habit
Chronic mouth breathing at night is associated with dry mouth, snoring and disturbed sleep, and there are good physiological reasons to prefer the nose. The right response for most people is to remove the obstacle rather than add a restraint: treat the allergies, clear the congestion, side-sleep, and get assessed if there is any suggestion of apnoea. Daytime practice helps too. If you spend the day breathing through your nose, the night tends to follow.
How to use this
- Make the nose your default at rest. Mouth closed, tongue on the roof of the mouth, breathing slow and low into the belly.
- Use nasal-only breathing to govern easy sessions. If you have to open your mouth, you are going too hard for a zone 2 day.
- Let the mouth open when it needs to. At high intensity this is correct physiology, not a failure.
- Fix the blockage rather than taping over it, and get snoring or daytime sleepiness properly assessed.
This article is for educational purposes and is not medical advice. Talk to your doctor before starting any new protocol, especially if you have a medical condition, take medication, or are pregnant. Daylight is a food supplement and nothing here is a claim about what it does.
