• Question: Why when i breathe out through my mouth it's hot but through my nose it is cold?

    Asked by bvbmonster to Davie, Gemma, James P, James V, Nuala on 25 Jun 2012.
    • Photo: James Verdon

      James Verdon answered on 25 Jun 2012:

      I’ve just tried this, but it’s not happening for me. However, I think I know why that might be happening. Your lungs are warm and wet, so the air you breathe out, which comes from the lungs, is warm and wet as well. When you breathe out through your mouth, the air comes out from your lungs, straight up your throat, through your mouth and out. There’s nowhere for that air to lose any heat or moisture, so when you breathe through your mouth it will be warm and wet.

      When you breathe out through your nose, the air has to go through all those narrow, twisty nasal passages. The heat and the moisture in the air you’re breathing out is captured by the tissues in your nasal passages, meaning that the air that is expelled is cooler and drier. I think this might be an adaptation to allow mammals to retain their body warmth, as we loose heat when we breathe out, as well as retaining moisture.

      At least, I think that’s the case, but I’m not a biologist, so perhaps find a biologist for a more accurate answer.

    • Photo: James Pope

      James Pope answered on 25 Jun 2012:

      Hi bvbmonster,

      I get a slight difference between mouth and nose temperature (at least on the back of my hand), but it changes if I breath out hard or soft (warmer when soft!).

      I’ll have to have a think, James V’s hypothesis (which is what we call a suggested solution in science) is good, but maybe there is a different one. I’ll get back to you if I can come up with one!

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