Smoke is a collection of airborne solid and liquid particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrained or otherwise mixed into the mass . It is commonly an unwanted by-product of fires (including stoves, candles , oil lamps , and fireplaces), but may also be used for pest control (fumigation), communication (smoke signals), defensive and offensive capabilities in the military (smoke screen), cooking , or smoking (tobacco, cannabis , etc.). Smoke is used in rituals where incense , sage, or resin is burned to produce a smell for spiritual purposes. Smoke is sometimes used as a flavoring agent, and preservative for various foodstuffs. Smoke is also a component of internal combustion engine exhaust gas, particularly diesel exhaust.
Smoke inhalation is the primary cause of death in victims of indoor fires. The smoke kills by a combination of thermal damage, poisoning and pulmonary irritation caused by carbon monoxide, hydrogen cyanide and other combustion products.
Smoke is an aerosol (or mist ) of solid particles and liquid droplets that are close to the ideal range of sizes for Mie scattering of visible light . This effect has been likened to three-dimensional textured privacy glass — a smoke cloud does not obstruct an image , but thoroughly scrambles it.