Pepper spray, also known as OC spray, OC gas, capsicum spray, or oleoresin capsicum is an inflamatry agent that irritates the eyes to cause tears, pain, and even temporary blindness. Pepper spray and other self defense sprays are used in riot control, crowd control, and personal self defense situations, including defense against dogs and bears. Also, the mucous membranes of the nose, throat, and sinuses burn, swell and make breathing difficult. In fact, even though tear gas is fairly nasty, it does not have the same inflammation and swelling effects of OC. Plus OC will not degrade over time like tear gas. People under the influence of drugs or who are otherwise oblivious to pain may be able to keep their eyes open when sprayed with tear gas but not so with OC (pepper spray). When sprayed in the eyes, the eyes will involuntarily slam shut whether they feel pain or not. However, OC will cause no lasting after effects. The effects last from 15 to 60 minutes. When sprayed, the temporary blindness causes fear and disorientation allowing you to escape and get help.

The active ingredient in pepper spray is capsiacin, which is a chemical derived from the fruit of plants in the Capsicum genus, including chilis. Scoville Heat Units (SHU) are used to measure the hotness of pepper spray. The Scoville Heat Scale is a measure of the hotness of a chili pepper. The number of Scoville heat units (SHU) in otherwords, indicates the amount of capsaicin present in a particular bottle of pepper spray. Some hot sauces use the Scoville rating in advertising as a selling point. 

The scale is named after its creator, American chemist Wilbur Scoville, who developed a test for rating the pungency of chili peppers. His method, which he devised in 1912, is known as the Scoville Organoleptic Test. Below is an example of the Scoville scale and its relationship with pepper spray: