Editing Smelling salts (section)

== Physiological action ==
[[File:Rembrandt van Rijn - Unconscious Patient (Allegory of Smell) - RR-111 - Leiden Collection.jpg|thumb|upright|[[Rembrandt]]'s ''[[The Senses (Rembrandt)|Unconscious Patient (Allegory of Smell)]]'' shows a woman using smelling salts to revive a man who has fainted at the hands of a [[barber-surgeon]].]]

Solid [[ammonium carbonate]] and [[ammonium bicarbonate]] salts partly dissociate to form {{chem|link=ammonia|NH|3}}, {{chem|link=carbon dioxide|CO|2}} and {{chem|link=water vapour|H|2|O}} vapour as follows:

{{block indent|{{chem2 | (NH4)2CO3 -> 2 NH3 + CO2 + H2O }}}}
{{block indent|{{chem2 | NH4HCO3 -> NH3 + CO2 + H2O }}}}

The smelling salts release ammonia ({{chem|NH|3}}) gas, which triggers an [[inhalation]] reflex. It causes the muscles that control breathing to work faster by irritating the [[mucous membrane]]s of the [[nose]] and [[lung]]s.<ref name=BBC1>{{cite news|work=BBC News|title=Henman's smelling salt solution|date=2002-07-02|url=http://news.bbc.co.uk/1/hi/health/2082231.stm|access-date=2009-01-03}}</ref>

Fainting can be caused by excessive [[parasympathetic nervous system|parasympathetic]] and [[vagus nerve|vagal]] activity that slows the [[heart]] and decreases [[perfusion]] of the [[brain]].<ref>{{cite web| url= http://www.webmd.com/heart-disease/tc/fainting-topic-overview | title= Fainting | website= WebMD| date= January 2, 2013 |access-date= April 22, 2014}}</ref> The sympathetic irritant effect is exploited to counteract these vagal parasympathetic effects and thereby reverse the faint.<ref>{{cite web| url= http://smellingsalts.org/why-do-smelling-salts-wake-you-up/|title=Why do smelling salts wake you up? |website= smellingsalts.org |date=7 July 2015|access-date=7 July 2015}}</ref>