Mist is a phenomenon caused by small droplets of water suspended in air. Physically, it is an example of a dispersion. It is most commonly seen where warm, moist air meets sudden cooling, such as in exhaled air in the winter, or when throwing water onto the hot stove of a sauna. It can be created artificially with aerosol canisters if the humidity and temperature conditions are right. It can also occur as part of natural weather, when humid air cools rapidly, notably when the air comes into contact with surfaces that are much cooler than the air.
The formation of mist, as of other suspensions, is greatly aided by the presence of nucleation sites on which the suspended water phase can congeal. Thus even such unusual sources as small particulates from volcanic eruptions, releases of strongly polar gases, and even the magnetospheric ions associated with polar lights can in right conditions trigger the formation of mist.
Mist is commonly confused with fog, which resembles a stratus cloud lying at ground level. These two phenomena differ, but share some commonalities; similar processes form both fog and mist. Fog is denser and generally lasts longer, while mist is thinner and more transparent.
Cloud cover is often referred to as "mist" when encountered on mountains, whereas moisture suspended above a body of water or marsh area is usually called "fog". One difference between mist and fog is visibility. The phenomenon is called fog if the visibility is 1 km (1,100 yd) or less. In the United Kingdom, the definition of fog is visibility less than 100 m (330 ft) for driving purposes, UK Highway Code rule 226, while for pilots the distance is 1 km. Otherwise, it is known as mist.
Mist makes a light beam visible from the side via refraction and scattering on the suspended water droplets.
"Scotch mist" is a light steady drizzle.
Mist usually occurs near the shores and is often associated with fog. Mist can be as high as mountain tops when extreme temperatures are low.
Freezing mist is similar to freezing fog, only the density is less and the visibility greater (when fog falls below 0 °C (32 °F), it is known as freezing fog).