# Why does my breath feel cool? **URL:** \ **Category:** Factual Questions\ **Created:** [August 8, 2018, 1:16pm UTC](https://boards.straightdope.com/t/why-does-my-breath-feel-cool/819274 "2018-08-08T13:16:10Z")\ **Posts on this page:** 5\ **Page:** 2
**Author:** ![Lance\_Turbo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lance_turbo/32/6156_2.png) [@Lance\_Turbo](https://boards.straightdope.com/u/Lance_Turbo)\ **Post date:** [August 8, 2018, 9:41pm UTC](https://boards.straightdope.com/t/why-does-my-breath-feel-cool/819274/21 "2018-08-08T21:41:07Z")
You guys keep showing that there is an effect and then claiming that there is no effect. 0.3 C is an effect. 1-2 degrees Fahrenheit is an effect. Gases cool off when they expand. That’s all. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [August 8, 2018, 9:46pm UTC](https://boards.straightdope.com/t/why-does-my-breath-feel-cool/819274/22 "2018-08-08T21:46:40Z")
> [@Lance\_Turbo](#): > > You guys keep showing that there is an effect and then claiming that there is no effect. > > 0.3 C is an effect. > 1-2 degrees Fahrenheit is an effect. > > Gases cool off when they expand. That’s all. Nobody said the effect is non-existent. I said it’s **insignificant**. And it would be **wrong** to say “your breath feels cool because the air cools as it expands.” Because that is **not** the reason behind this observation. There are at least 2 other mechanisms at play (as already explained) that are more relevant. ---
**Author:** ![Lance\_Turbo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lance_turbo/32/6156_2.png) [@Lance\_Turbo](https://boards.straightdope.com/u/Lance_Turbo)\ **Post date:** [August 8, 2018, 9:54pm UTC](https://boards.straightdope.com/t/why-does-my-breath-feel-cool/819274/23 "2018-08-08T21:54:18Z")
> [@scr4](#): > > And it would be **wrong** to say “your breath feels cool because the air cools as it expands.” Because that is **not** the reason behind this observation. There are at least 2 other mechanisms at play (as already explained) that are more relevant. It’s a good thing that nobody claimed that then. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [August 9, 2018, 2:36am UTC](https://boards.straightdope.com/t/why-does-my-breath-feel-cool/819274/24 "2018-08-09T02:36:53Z")
> [@Lance\_Turbo](#): > > You guys keep showing that there is an effect and then claiming that there is no effect. That claim is unsupported. In fact, it’s contradicted. Although several posts above this one agree there is an effect, none of the posts above this one claims there is no effect. > [@Lance\_Turbo](#): > > Gases cool off when they expand. That’s all. Yeah, you said that. And several of us agreed with you that there is an adiabatic cooling effect as the air goes from elevated pressure in your mouth to ambient pressure outside your mouth. We also pointed out that this _must_ be preceded by an adiabatic _heating_ effect when you first elevate the pressure in your respiratory tract that tends to cancel it out (although there may or may not be meaningful heat transfer from that air to lung tissues in the intervening period, depending on the magnitude of the initial pressure increase and the total residence time in the respiratory tract). Do you disagree with that? I further pointed out a method by which you can demonstrate to yourself that the effect of entraining cool, dry ambient air into the plume issuing forth from your mouth is far and away the dominant effect in the observed cooling sensation - to the point that _eliminating_ that entrainment results in an observed _heating_ sensation because the air exiting your mouth is warmer than your skin. This is especially true under the casual, low-pressure blowing scenarios being considered by the OP. In other words, any _net_ adiabatic effect (heating + cooling) under those scenarios is _insignificant_ compared to the convective (and augmented evaporative) cooling provided by ambient air entrainment. Do you disagree with that? ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [August 9, 2018, 1:24pm UTC](https://boards.straightdope.com/t/why-does-my-breath-feel-cool/819274/25 "2018-08-09T13:24:42Z")
> [@The\_wind\_of\_my\_soul](#): > > Does anyone know why pursing your lips helps control shortness of breath? **Machine Elf** , you were good with the last question, maybe you can answer this one, too? Hadn’t heard this before, but like you I did a quick Google search and found a Wikipedia page on [pursed-lip breathing,](https://en.wikipedia.org/wiki/Pursed_lip_breathing) which says that the slight elevation in respiratory tract pressure helps to force airways open, making it easier to move air through them. ISTM this would actually make exhaling require _more_ work (since you’re exhaling through a restriction), but perhaps the trade-off is that the airways remain in this forced-open state during inhalation, which would reduce inhalation effort. Would be interested to hear from a doctor (especially a respiratory specialist) on this one. When I have a sinus cold and struggle to breathe through my nose, I do something similar. I plug my nose with my fingers and do a [Valsalva maneuver,](https://en.wikipedia.org/wiki/Valsalva_maneuver) forcing my swollen sinuses to open up. This opened-up condition lasts just long enough to get in a couple of good, forceful inhalations through my noise, helping to clear out some gunk. [Previous page](https://boards.straightdope.com/t/why-does-my-breath-feel-cool/819274.md?page=1)