The breath in our mouth contains water, which is a colorless and transparent gaseous water. In winter, the gas in the mouth comes out of the warm mouth and meets the air. At this time, the air is much colder. Therefore, after the gas in the mouth is cooled, it will immediately condense into small water droplets, and the small water droplets will get together and look like white gas. The temperature is very high in summer, so the gas ejected from the mouth will not condense into small water droplets, and we will not see "white gas".

When watching a performance, we can often see a "white smoke" on the stage. This kind of white smoke is not made of water vapor, but a masterpiece of dry ice.

Dry ice is solid carbon dioxide. Under normal circumstances, we can't see liquid carbon dioxide, and solid carbon dioxide will sublimate directly into gas. At normal temperature and pressure, carbon dioxide is gaseous. At low temperature or high pressure, carbon dioxide becomes solid, shaped like ice and snow. Dry ice sprayed on the stage will heat up and sublimate into carbon dioxide. When dry ice sublimes, it will absorb a lot of heat and make the surrounding temperature drop rapidly. The water vapor in the low temperature area will liquefy into small water droplets, and many small water droplets will gather together and float in the air, becoming "white smoke".