How do you know it’s cold without checking the weather forecast? When people open their mouths and exhale clear puffs of breath. It’s a well-known fall and winter phenomenon, but how does it actually arise? We explain.

water vapor when breathing

It starts with your breathing. When you breathe in, a small amount of water vapor is released. This comes from the lungs and airways. You won’t see this water vapor at room temperature or in warm weather outside. Then the temperature is so high that the water does not take a solid form, but appears as a gas. No respiratory cloudiness is clearly visible.

Less than 7 degrees? A chance to catch a breath

But if the temperature drops below 7°C and the air is humid, the chance of this happening increases a lot. Then the warm water vapor can come into direct contact with the cold air. The water vapor cools, solidifies, and becomes visible. This is how the well-known breathing draws are formed when you exhale.

Have you been outdoors longer? Less chance of breathing clouds

At least this is the case if you have just moved from a warm room to a cold one. For example, if you go from indoors to outdoors, your breath will be warmer than the air outside. But if you are outside or in a cool room for a longer period of time, your breath will also get colder due to the lower temperature. If you then breathe in cold air, you exhale cold air again. And a cool breath retains less moisture than a warm breath, so you emit fewer breath draws if you’re in a cold room for a longer time.

Airplanes also produce ‘breathing clouds’.

Most breathing clouds disappear instantly, unless you blow them on a window or mirror. Then they remain in the form of condensation. The lines that aircraft leave during flight are constructed according to a similar principle. Aircraft exhaust gases contain not only soot particles, but also water vapor. Since airplanes often fly through very cold, moist air, warm water vapor lingers for a long time. So the lines of the plane are actually very large and elongated “breathing clouds”.

Read also: Do you always suffer from cold hands? Try these breathing techniques

(Source: Willem Wever, Quest, Youth, Culture & Science, KNMI. Photo: Shutterstock)