The usual active compound is ammonium carbonate, a colorless-to-white, crystalline solid ((NH4)2CO3).[1] Because most modern solutions are mixed with water, they should more properly be called "aromatic spirits of ammonia."[1] Modern solutions may also contain other products to perfume or act in conjunction with the ammonia, such as lavender oil or eucalyptus oil.[2]
Historically, smelling salts have been used on people feeling faint,[3][4][5] or who have fainted. They are typically administered by others, but may be self-administered; some at-risk groups, such as pregnant women, may be advised to keep them close to hand.[6]
Smelling salts are often used on athletes (particularly boxers) who have been dazed or knocked unconscious to restore consciousness and mental alertness.[1]