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DennyRombardt t1_ixnqvq7 wrote

If you close your mouth, you just breathe through your nose. If you open your mouth, you breathe through your mouth and nose. If you have a perforated ear drum, you can breathe through your ears. When you breathe in, air will enter through any orifice available unless you physically block it yourself. Your body has no way to do it. Apart from obviously closing your mouth.

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DennyRombardt t1_ixo1fsb wrote

Replying to SteptimusHeap (#656,976)

It doesn't. It blocks air coming in from your mouth. You can have your mouth open and only breath through your nose. Your epiglottis and tonsils close up at the back of your throat to block it. There is no internal way for you to block your nose.

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uh-okay-I-guess t1_ixob8wh wrote

Just to address the other answer, the epiglottis prevents food from entering your trachea. It doesn't help direct air between your mouth and nose. It is not anywhere near the right location to do that.

The palate and tongue can make a seal that blocks off the mouth, forcing all air to move through your nose (even when your mouth is open).

The soft palate can't fully block off the nasopharynx in normal people, so there's always at least some air coming through the nose, but with a wide-open mouth and lifted soft palate, chances are more air is going to move through the mouth.

In [1], when subjects were not exercising, some breathed only through their noses, while others breathed partly through their mouths; however, even in the mouth breathers, 70% of the air came through their noses. When the subjects were exercising hard, everyone used their mouth. The proportion of air passing through the mouth reached 70% in habitual "mouth breathers" but only 60% in habitual nose breathers. This is probably because people who habitually breathe through their mouths have higher nasal resistance.

[1] Niinimaa et al., "Oronasal distribution of respiratory airflow" (1981), https://pubmed.ncbi.nlm.nih.gov/7244427/

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