Capsaicinoids are the name given to the class of compounds found in members of the capsicum family (also known as peppers). The most common capsaicinoid is capsaicin. The Scoville Scale is a measurement of capsaicin concentration reported in Scoville heat units (SHU).
Capsaicinoids give chile peppers their heat and are present in almost every pepper. They are found primarily in the pepper’s ribs and seeds, making these parts hotter than the rest of the pepper. Consequently, you can reduce the amount of heat you get from a pepper by removing the ribs and seeds.
Capsaicinoids have no flavor or odor but act directly on the pain receptors in the mouth and throat.
Capsaicinoids are produced by peppers as a deterrent against certain mammals and fungi. It is an irritant for most mammals, including humans. It produces a sensation of burning in any tissue with which it comes into contact. This is to discourage critters from eating them. Birds, however, are an exception. Birds are not affected by capsaicin. This is why many small, upright varieties of peppers are called Bird Peppers. Because birds are known to eat them.
One study showed that chile pepper seed germination is decreased in the GI tract of mammals but not by the passage through the GI tract of birds. Therefore, birds can benefit from the nutritional value of the chile peppers by not being sensitive to the capsaicin. The plant benefits by getting the seeds dispersed efficiently.
Capsaicin has many uses.
It is used medically to produce deep-heating rubs for treating sports injuries and arthritic therapies.
Some use it as an animal repellent for cats, squirrels, skunks, and raccoons. The capsaicin irritates animals when they touch, smell or taste the product, keeping them out of yards or flowerbeds.
Please note: The National Pesticide Information Center advises against the use of capsaicin, which kills honeybees and other beneficial insects, so it might not be the best thing to spray outdoors.
It’s also used for self-defense in pepper spray, also known as OC spray (from “oleoresin capsicum”), OC gas, or capsicum spray.