Smelling salts are a type of chemical compound used as stimulants to restore consciousness after fainting. They have been used since the 13th century as a medicinal tool to prevent or remedy fainting. Smelling salts are made of a chemical, usually ammonia, that has a very strong smell. When the smelling salts are put under the nose of someone who has fainted, the sharp smell causes them to wake up again. The fumes from smelling salts are harsh and irritate the interior of the nose, causing the lungs to quickly breathe deeply to clear the nasal passage. The fumes trigger a breathing reflex, which helps restart respiratory rhythms and send oxygen to the brain.

Smelling salts are typically used to revive people who have fainted or who feel lightheaded and dizzy. They are also used by athletes (particularly boxers) who have been dazed or knocked unconscious to restore consciousness and mental alertness. Smelling salts are now banned in most boxing competitions.

The primary benefit of smelling salts is to resuscitate someone who has fainted. Athletic trainers have found alternative uses for smelling salts, such as treating head injuries. However, overuse of smelling salts may lead to damage to nasal passages, and concentrated exposure can damage the upper airways and lungs and cause allergic reactions. While smelling salts are generally safe when used as directed, prolonged inhalation may result in permanent lung damage or death.