# "Seeing your breath" in warm weather **URL:** \ **Category:** Factual Questions\ **Created:** [July 27, 2009, 6:42pm UTC](https://boards.straightdope.com/t/seeing-your-breath-in-warm-weather/504462 "2009-07-27T18:42:00Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![likethedirection](https://avatars.discourse-cdn.com/v4/letter/l/b2d939/32.png) [@likethedirection](https://boards.straightdope.com/u/likethedirection)\ **Post date:** [July 27, 2009, 6:42pm UTC](https://boards.straightdope.com/t/seeing-your-breath-in-warm-weather/504462/1 "2009-07-27T18:42:00Z")
My boyfriend keeps telling me that he was able to see his breath when he hiked to the top of the Arenal Volcano in Costa Rica. He said it was very warm up there. The tour guide said it was due to the low oxygen levels but I’m having a hard time believing it. Does anyone know why this might have occurred? ---
**Author:** ![Spud](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/spud/32/347_2.png) [@Spud](https://boards.straightdope.com/u/Spud)\ **Post date:** [July 27, 2009, 7:32pm UTC](https://boards.straightdope.com/t/seeing-your-breath-in-warm-weather/504462/2 "2009-07-27T19:32:57Z")
Maybe he should consider a breath mint. Sorry, I got nuthin. I didn’t know you could hike to the top of it though… it is a very active volcano (and a beautiful one at that). The eruption we saw I wouldn’t have wanted to be on the top at the time. ---
**Author:** ![OldGuy](https://avatars.discourse-cdn.com/v4/letter/o/3bc359/32.png) [@OldGuy](https://boards.straightdope.com/u/OldGuy)\ **Post date:** [July 27, 2009, 8:07pm UTC](https://boards.straightdope.com/t/seeing-your-breath-in-warm-weather/504462/3 "2009-07-27T20:07:03Z")
When you see your breath you are seeing water vapor condensing out; that is, you’re seeing a miniature fog. Since cold air holds less water vapor than warm air, you typically see your breath when it’s cold outside and the water vapor in your warm breath condenses out. This is similar to your glasses “steaming up” if you come out of the cold. Your cold glasses chill the air immediately around them and the vapor condenses out. I don’t know why low oxygen per se would do anything. He may have meant the air was rarefied. Rarefied air probably can hold less water vapor as well so it again may condense out of your breath. But that is a bit of a guess. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [July 27, 2009, 8:25pm UTC](https://boards.straightdope.com/t/seeing-your-breath-in-warm-weather/504462/4 "2009-07-27T20:25:11Z")
> [@OldGuy](#): > > Rarefied air probably can hold less water vapor as well so it again may condense out of your breath. But that is a bit of a guess. A good guess, but seemingly wrong: > [@](#): > > Saturation water vapor pressure of air-water mixtures shows a very slight dependence on system pressure. The empirical equations of Buck[10] show that the difference in water vapor pressure between normal atmospheric pressure and no air at all is about 0.4% at room temperature. This is equivalent to the vapor pressure change from a temperature decrease of less that 0.1°C. > **[Humidity | Pressure dependence](https://en.wikipedia.org/wiki/Relative_humidity#Pressure_dependence)** > > The relative humidity of an air–water system is dependent not only on the temperature but also on the absolute pressure of the system of interest. This dependence is demonstrated by considering the air–water system shown below. The system is closed (i.e., no matter enters or leaves the system). A slightly different guess is that the lower pressure on top of the mountain results in the air coming out of your mouth being more saturated than it is at lower altitude, i.e. an effect of pressure on evaporation rate. That could get your breath to steaming at higher temps than normal.