Question Why do I see my breath when it's cold outside?
Cold air causes the warm moisture in our breath to condense into tiny droplets of water that appear like a small, misty cloud.
Because our bodies contain nearly 70% water, the air in our lungs is almost completely saturated with water vapor (water in gas form) and is the same temperature as our bodies (98.6oF). Cold air cannot hold as much moisture as warm air. So when one exhales a warm, saturated breath on a cold day the cold air rapidly lowers the temperature of our breath, whereupon the combination briefly reaches dew point. At dew point, air can no longer hold water vapor; when air is cooled beyond dew point water vapor turns to liquid form, the physical process known as condensation. It is this liquid form of your breath – minuscule droplets of water – that creates the fleeting, misty cloud we see when breathing in cold weather.
Seeing your breath requires just the right combination of temperature and humidity. Though it is pretty common to see your breath in cold weather (usually below 45oF), the next time you have fun making breath clouds, you’ll know it’s because of the exact science of atmospheric moisture and temperature.
Published: 11/19/2019. Author: Science Reference Section, Library of Congress