Smelling salts, also known as spirit of hartshorn or sal volatile, are chemical compounds used for arousing consciousness.[1] The usual active compound is ammonium carbonate, a colorless-to-white, crystalline solid ((NH4)2CO3·H2O).[1][2] 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 eucalyptus oil.[3]
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Smelling salts have been used since Roman times, and are mentioned in the writings of Pliny as 'Hammonicus sal',[1]. Evidence exists of use in the 13th century by alchemists as 'sal ammoniac'.[1]
In the 17th century, an ammonia solution was distilled from shavings of harts' (deer) horns and hooves, which led to the alternative name for smelling salts as spirit or salt of hartshorn.[1]
Smelling salts have also been known as 'sal volatile', for their ability to produce a reaction.[4]
They were widely used in Victorian Britain to revive fainting women, and in some areas constables would carry a container of them for the purpose.[5]
The use of smelling salts was widely recommended during the Second World War, with all workplaces advised by the British Red Cross and St. John Ambulance to keep 'sal volatile' in their first aid boxes.[6]
Smelling salts are often used on athletes (such as boxers) when they are knocked unconscious or semi-conscious[1] (although a number of sports governing bodies, such as the Football Association in the UK recommend against their use[7]).
They are also used in competitions (such as strong man and Ice hockey) to "wake up" competitors to perform better.[1][8]
They are also still used for people feeling faint,[9][10][11] or who have fainted, either administered by others, or self administered, with some at risk groups, such as pregnant women, sometimes advised to keep them close to hand.[12]
Smelling salts release ammonia (NH3) gas, which irritates the mucous membranes of the nose and lungs, and thereby triggers an inhalation reflex[8] (that is, it causes the muscles that control breathing to work faster[8]).
Ammonia gas is toxic in large concentrations for prolonged periods,[1] and can be fatal.[11] Smelling salts produce only a small amount of ammonia gas.[1]
There is a limited possibility of direct burning of the nasal or oral mucosa from high concentration of inhaled ammonia.[1]
The use of ammonia smelling salts to revive people injured during sport is not recommended as it may inhibit or delay a proper and thorough neurological assessment by a healthcare professional,[1] and some governing bodies recommend specifically against it.[7] There is also a risk that as an irritant, use of smelling salts could cause reflex withdrawal from the source, thereby exacerbating any pre-existing cervical spine injury.[1]