Tear gases are gaseous substances or aerosols that cause strong irritations and pain in the eyes, producing a flow of tears. At the same time, it becomes difficult to keep the eyes open. A further effect is a burning sensation in the mouth, throat and respiratory tract. High concentrations of tear gas produce breathing difficulties and pressure on the chest. Vomiting may also result. A burning, prickling sensation may be experienced on the skin. Warm moist skin reacts more strongly, and inflammations may occur. In high concentrations, tear gases can be dangerous for people with allergies, for the elderly, for those with heart or lung defects, for children and for pregnant women. If exposure occurs in enclosed places, and at high concentrations, the consequences can be serious, even fatal.
Ordinary tear gas (CN, or chloracetophenone) is used in riot control and civilian police uses. An emetic and respiratory agent known as adamsite or DM is another older short-term incapacitant. For military purposes, the principal agent used is the harassing agent CS (orthochlorobenzalmalonitrile). It is dispersed as an aerosol by vaporizing the agent from a pyrotechnic mixture, hence its use in grenades, rockets, artillery shells and cluster bombs. A newer form CS-2 is dispersed as an even finer and persistent aerosol, and can stay effective for several weeks as it is reintroduced into the air by wind and personnel movements.