Editing Referred pain (section)

===Algogenic substances===
In recent years several different chemicals have been used to induce referred pain including bradykinin, [[substance P]], [[capsaicin]],<ref name="pmid10666547">{{cite journal |vauthors=Witting N, Svensson P, Gottrup H, Arendt-Nielsen L, Jensen TS |title=Intramuscular and intradermal injection of capsaicin: a comparison of local and referred pain |journal=Pain |volume=84 |issue=2–3 |pages=407–12 |year=2000 |pmid=10666547 |doi=10.1016/S0304-3959(99)00231-6|s2cid=27403703 }}</ref> and [[serotonin]]. However, before any of these substances became widespread in their use a solution of hypertonic [[saline (medicine)|saline]] was used instead. Through various experiments it was determined that there were multiple factors that correlated with saline administration such as infusion rate, saline concentration, pressure, and amount of saline used. The mechanism by which the saline induces a local and referred pain pair is unknown. Some researchers have commented that it could be due to osmotic differences, however that is not verified.<ref name=ArendtNeilsen/>