# Breathing out smoke when it's cold - Explanation?

**URL:** <https://boards.straightdope.com/t/breathing-out-smoke-when-its-cold-explanation/332769>\
**Category:** Factual Questions\
**Created:** [November 26, 2005, 3:03am UTC](https://boards.straightdope.com/t/breathing-out-smoke-when-its-cold-explanation/332769 "2005-11-26T03:03:27Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Revenant\_Threshold](https://avatars.discourse-cdn.com/v4/letter/r/f1d935/32.png) [@Revenant\_Threshold](https://boards.straightdope.com/u/Revenant_Threshold)\
**Post date:** [November 26, 2005, 3:03am UTC](https://boards.straightdope.com/t/breathing-out-smoke-when-its-cold-explanation/332769/1 "2005-11-26T03:03:27Z")

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Yes, I know it isn’t smoke - I just couldn’t think of a better word to describe it. I’m assuming it has something to do with condensation, and that in fact it’s just the normal water vapour we breathe out but visible for some reason due to the cold?

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**Author:** ![St\_Ides](https://avatars.discourse-cdn.com/v4/letter/s/ccd318/32.png) [@St\_Ides](https://boards.straightdope.com/u/St_Ides)\
**Post date:** [November 26, 2005, 3:05am UTC](https://boards.straightdope.com/t/breathing-out-smoke-when-its-cold-explanation/332769/2 "2005-11-26T03:05:07Z")

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It’s the moisture in your breath cooling to below its dewpoint, and condensing, making it visible. Same way a cloud is formed.

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**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\
**Post date:** [November 26, 2005, 3:22am UTC](https://boards.straightdope.com/t/breathing-out-smoke-when-its-cold-explanation/332769/3 "2005-11-26T03:22:11Z")

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Here’s a recent thread on seeing your breath:  
[How cold must it be to see your breath?](http://boards.straightdope.com/sdmb/showthread.php?t=340204)

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**Author:** ![pretend\_my\_name\_is\_witty](https://avatars.discourse-cdn.com/v4/letter/p/b9e5f3/32.png) [@pretend\_my\_name\_is\_witty](https://boards.straightdope.com/u/pretend_my_name_is_witty)\
**Post date:** [November 26, 2005, 2:59pm UTC](https://boards.straightdope.com/t/breathing-out-smoke-when-its-cold-explanation/332769/4 "2005-11-26T14:59:40Z")

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Bill Hicks said he loved seeing all the smokers in Chicago pass out in winter, 'cause they dont realise when they’re done exhaling…brilliant.

Living in Glasgow now, realise what he meant properly, it’s confusing!

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**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\
**Post date:** [November 26, 2005, 4:06pm UTC](https://boards.straightdope.com/t/breathing-out-smoke-when-its-cold-explanation/332769/5 "2005-11-26T16:06:38Z")

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Look up in the sky; you see clouds. They’re suspensions of condensed water droplets in the air.

When low clouds touch the ground, they become fog. Same thing: water droplets suspended in the air.

The air contains water vapor. The warmer the air is, the more it has the potential to contain. Your exhalations are N% relative humidity at lung temperature, and in typical summer weather there’s quite sufficient absorption capacity in the air to accept the water vapor content of your exhalation as the temperature drops from lung temperature (say 95 F/36 C on a guess) to the 70 F/ 21 C ambient temperature of your surroundings.

But when the temperature drops to winter levels, its capacity to absorb water vapor drops dramatically. And your exhalations cooling from 95 F/36 C to 32 F/0 C suddenly are overloaded with water vapor, and it condenses out as an evanescent fog.