Oleoresin capsicum (OC or "pepper spray"; not to be confused with "Mace," a commercial brand of CN in aersol form) is a riot control agent used primarily by law enforcement agencies and was not an agent standardized by the US military (OC is an abbreviation, not a chemical agent code). This agent was in US military inventory for use by military police for incapacitating violent or threatening subjects, but also has applications for special forces and stability and support operations.
OC is a naturally occurring substance found in the oily resin of cayenne and other varieties of peppers, but can and is also be produced synthetically. As a result, the various grades of OC are often described using the Scoville scale developed by Wilbur Scoville in 1912 for measuring the "heat" of peppers. Sprays intended for use on humans are rated generally between 200,000 and 2,000,000 Scoville Heat Units (SHUs), while the hottest peppers generally range from 350,000 to 1,500,000 SHUs. Sprays intended for protection against large animals, such as bears (leading to the colloquial term "Bear Mace", though again not to be confused with Mace), come in grades sometimes over 9,000,000 SHUs. Pure capsaicin is rated at 15,000,000 to 16,000,000 SHUs.
Contact with OC particles in a sprayed mist incapacitates subjects by inducing an almost immediate burning sensation of the skin and burning, tearing, and swelling of the eyes. When inhaled, the respiratory tract becomes inflamed causing the mucous membranes to swell. This restricts breathing to short, shallow breaths.
Standard RCAs like CS or CR also cause tearing and respiratory discomfort (irritant effects), but do not induce the inflammation and swelling effects of OC. OC is most commonly dispersed via a hand-held canister similar to M32/36 dispersers and when sprayed most people cannot keep their eyes open unless they physically hold their eyelids apart due to the swelling. Fear and disorientation often result from this temporary blindness. Affected personnel may also lose strength and coordination due to the shortness of breath.