Capsaicin

Scoville scale

Capsaicin [kap-sey-uh-sin] is a chemical substance. It is responsible for the sense of hotness found in chile peppers. In mammals, it causes a sensation of burning of the tissues it comes in contact with. Capsicain, and other similar substances called capsaicinoids are produced by chile peppers and other plants, probably as deterrents against certain herbivores and fungi. Pure capsaicin is a hydrophobic, colorless, odorless, crystalline to waxy compound.

Capsaicinoids are added to food to make it have a hot taste, but it can also be used as an analgesic (painkiller). Such painkillers are often directly used on the skin. The burning of the capsaicin masks the real pain. Capsicaicin is also the main agent in pepper spray. Capsicain is not soluble in water; it binds to oil and fat. Soap can be used to wash it off. In 2006, it was discovered that the venom of a certain tarantula species activates the same pathway of pain as is activated by capsaicin, the first demonstrated case of such a shared pathway in both plant and animal anti-mammal defense.

Capsaicin is present in large quantities in the placental tissue (which holds the seeds), the internal membranes and, to a lesser extent, the other fleshy parts of the fruits of plants in the genus Capsicum (peppers). The seeds themselves do not produce any capsaicin, although the highest concentration of capsaicin can be found in the white pith of the inner wall, where the seeds are attached. The seeds of Capsicum plants are predominantly dispersed by birds, which do not react to capsaicin. Chili pepper seeds consumed by birds pass through the digestive tract and can germinate later, but mammals have molar teeth, which destroy seeds and prevent them from germinating. Thus, natural selection may have led to increasing capsaicin production because it makes the plant less likely to be eaten by animals that do not help it reproduce. In addition, there is evidence that capsaicin evolved as an anti-fungal agent. The fungal pathogen, Fusarium, is known to infect wild chilies which reduces seed viability. Capsaicin deters the fungus, and in doing so limits this form of predispersal seed mortality.

It is common for people to experience pleasurable and even euphoriant effects from ingesting capsaicin. Folklore among self-described ‘chiliheads’ attributes this to pain-stimulated release of endorphins, a different mechanism from the local receptor overload that makes capsaicin effective as a topical analgesic. In support of this theory, there is some evidence that the effect can be blocked by naloxone and other compounds that compete for receptor sites with endorphins and opiates. According to animal and human studies, the oral intake of capsaicin may increase the production of heat by the body for a short time. Due to the effect on the carbohydrates breakdown after a meal, cayenne may also be used to regulate blood sugar levels. Further research is required to see if capsaicin would be useful to treat obesity.

Clifford Woolf, the Richard J. Kitz Professor of Anesthesia Research at Harvard Medical School, has suggested using capsaicin to deter abuse of certain extended-release drugs such as OxyContin and Ritalin. When taken as prescribed, opioid prescription drugs such as OxyContin or stimulant drugs such as Adderall XR release their active chemical over time, but when crushed and insufflated, taken as a suppository, chewed, or injected, the larger than normal dosage is absorbed all at once and a much stronger effect is produced that can be highly habit-forming and potentially fatal due to the higher risk of overdose. Woolf has argued that adding capsaicin into the capsules would be a safe way to deter abuse. A person taking the capsule in the prescribed way (i.e., swallowing it whole) would suffer no ill effects from the additive. However, a person crushing it would expose the irritant. Anyone then chewing it, snorting it, or injecting it would be exposed to the full power of the chemical. ‘Imagine snorting an extract of 50 jalapeño peppers and you get the idea,’ Woolf said.

Capsaicin is also the active ingredient in riot control and personal defense pepper spray chemical agents. When the spray comes in contact with skin, especially eyes or mucous membranes, it is very painful, and inhaling small particles of it as it disperses can cause breathing difficulty, which serves to discourage assailants. In large quantities, capsaicin can cause death. Symptoms of overdose include difficulty breathing, blue skin, and convulsions. The large amount needed to kill an adult human and the low concentration of capsaicin in chilies make the risk of accidental poisoning by chili consumption negligible. Capsaicin is also used to deter mammalian pests. A common example is the use of ground-up or crushed dried chili pods in birdseed to deter squirrels, since birds are unaffected by capsaicin. Capsaicin is a banned substance in equestrian sports because of its hypersensitizing and pain relieving properties. At the show jumping events of the 2008 Summer Olympics, four horses tested positive for the substance, which resulted in disqualification.

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