Effects and use of tear gas
Tear gas works by irritating mucous membranes in the eyes, nose, mouth and lungs, and causes crying, sneezing, coughing, hard breathing, pain in the eyes, temporary blindness, etc. Lachrymators are thought to act by attacking sulphydryl functional groups in enzymes. One of the most probable protein targets is the TRPA1 ion channel that is expressed in sensory nerves (trigeminal nerve) of the eyes, nose and mouth. First used in 1915, xylyl bromide was a popular tearing agent since it was easily brewed.
Lachrymatory agents are commonly used as riot control and chemical warfare agents. During World War I, more toxic lachrymatory agents were used. Certain lachrymatory agents are often used by police to assist in bringing targeted persons under control, most notably tear gas. In some countries (e.g. Finland, Australia, and the United States), another issued substance is mace, which is used as a personal attack repellent.