Why is air from the mouth more humid than from the nose?


Oftentimes I notice any exhalation from the mouth turn to a visible mist, but that doesn’t happen when exhaling from the nose. Is there something capturing moisture in the nasal cavity, or is it just that more moisture comes from the mouth itself?

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Nose air and mouth air carry the same humidity. Perceived differences in humidity could be due to several factors.

First of all your nostrils point down, meaning exhaled condensation doesn’t occupy as much of your vision.

Second, the nostrils are smaller than your mouth, meaning the same volume of air must move faster to exit your nose than from your open mouth. Faster air disperses quicker, meaning the condensation cloud that forms fills a wider area and so appears less dense. Finally, fast moving air leaves a less condensation on surfaces, since the moving air also speeds evapouration, meaning less of its humidity condenses onto any particular surface.

If you wear glasses, the next time you blow on the lenses to wipe them, compare the condensation left behind after blowing through an open mouth against what forms by blowing through pursed lips that form a nostril-sized hole.

I suspect the open mouth will deposit more condensation onto your lenses.