Pepper spray, also known as OC spray (from "Oleoresin Capsicum"), OC gas, and capsicum spray, is a lachrymatory agent (a chemical compound that irritates the eyes to cause tears, pain, and even temporary blindness) that is used in riot control, crowd control, and personal self-defense, including defense against dogs and bears. It is a less lethal agent that may be deadly in rare cases. As of 1995, the American Civil Liberties Union documented 26 individuals subject to police action who died following exposure to pepper spray. In none of these cases was pepper spray listed as the cause of death, but it is unclear whether it may have been a contributing factor in some cases.[1] The active ingredient in pepper spray is capsaicin, which is a chemical derived from the fruit of plants in the Capsicum genus, including chilis. Long-term effects of pepper spray have not been effectively researched.[citation needed]

Extraction of oleoresin capsicum from peppers involves finely ground capsicum, then the capsaicin is extracted in an organic solvent such as ethanol. The solvent is then evaporated, and the remaining waxlike resin is the oleoresin capsicum. An emulsifier such as propylene glycol is used to suspend the OC in water, and pressurized to make it aerosol in pepper spray. The high performance liquid chromatography (HPLC) method is used to measure the amount of capsaicin within pepper sprays. Scoville Heat Units (SHU) are used to measure the concentration or "heat" of pepper spray.

Oleoresin capsicum also is used in foods where the flavor and piquancy are desired without visible pepper specks, or to standardize the Scoville units.[citation needed]

A synthetic analogue of capsaicin, pelargonic acid vanillylamide (desmethyldihydrocapsaicin), is used in another version of pepper spray known as PAVA spray which is used in England. Another synthetic counterpart of pepper spray, pelargonic acid morpholide, was developed and is widely used in Russia. Its effectiveness compared to natural pepper spray is unclear.

Pepper spray typically comes in canisters, which are often small enough to be carried or concealed in a pocket or purse. Pepper spray can also be bought concealed in items such as rings. There are also pepper spray projectiles available, which can be fired from a paintball gun. It has been used for years against demonstrators.