Smelling salts were once commonly used to relieve faintness and headaches. The salts are made up of ammonium carbonate mixed with perfume. This drug is known as a stimulant. The ammonia fumes from the salts irritate the membranes of the nose and lungs. This irritation results in a reflex that causes the muscles controlling breathing to work faster.
Doctors no longer recommend smelling salts. Some athletes claim using the salts before competing makes them more alert. This use of smelling salts is probably neither helpful nor harmful. Some athletes also use smelling salts after a head injury, incorrectly believing the salts counteract the effects of the injury. Doctors caution against this usage and advise seeking medical treatment for any head injury, even if the injury seems minor.
See also Ammonia.