2-(4-Chlorobenzylidene)malononitrile, commonly known as CS gas, is a synthetic chemical compound used as a riot control agent. It acts as a potent lacrimator and irritant, causing intense burning sensations in the eyes, skin, and respiratory tract upon exposure. Effects include involuntary eye closure, excessive tearing, coughing, and difficulty breathing, which temporarily incapacitate individuals without causing permanent harm. CS is typically deployed via aerosol canisters or grenades by law enforcement for non-lethal crowd control and has been widely studied for its rapid onset and reversible effects. It is not commonly used in civilian self-defense sprays, which are usually based on oleoresin capsicum (pepper spray).