I have this weird but reproducible thing that I can see my breath for less than a second even in hot/humid weather. The key to do that is to pop my ears - I have to do that often, it's like I'm on a flight, not sure why my ear is that way... Anyway even if I just try to force more air into my mouth, keeping it flexed (not blowing it up like a balloon)... At the moment I open mouth and let the air out I can see it. I noticed it on a hot day in the car, against the darkness of the dashboard I could see the vapor. Also just about anywhere, anytime. It's barely visible though. My friend can see his breath during or after rain (!)... I think it has something to do with pressure and relative humidity - but then why does it work in very humid weather too, also in the bathroom? If I breath out normally it does not happen at all! I'd like to know the scientific explanation (and if it's normal or there is something wrong with me).

  • $\begingroup$ that is interesting semi related is I can repeatedly pop my right big toe $\endgroup$ – Little Bowsette Jan 29 at 23:55

The relative humidity of air is pressure dependent. Your method of popping your ears involves increasing the pressure of the air in your mouth. And if you sufficiently compress a volume of air that has a high relative humidity, you can increase the air's relative humidity beyond it's saturation limit, which causes the water vapor in the air to start to condense, producing a visible mist.

You can find videos and descriptions of this phenomenon by googling "mouth mist trick".

  • $\begingroup$ And there's the related fact that when you lower the pressure you lower the temperature--and what happens when you lower the temperature of saturated air? Condensation. $\endgroup$ – Loren Pechtel Sep 20 '14 at 4:22

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