Histamines were substances associated with allergies.
When Doctor Seth Mendoza was infected with Ferengi pyrocytes in 2366, his immune system responded with a system-wide histaminic reaction. (TNG: "The Price")
An early symptom of infection by the Tarchannen III species is an allergic histamine response. (TNG: "Identity Crisis")
In Iresine syndrome, patients exhibit electropathic residue and lowered histamine count. The absence of lowered histamine levels permit the aftereffects of Ullian telepathic memory invasion to be distinguished from Iresine syndrome. (TNG: "Violations")