Capsaicin
The chemical compound capsaicin (8-methyl N-vanillyl 6-nonenamide) is the active component of chili peppers (Capsicum). It is an irritant to mammalian epithelial cells and produces a burning sensation in the mouth, which some people enjoy. Plants produce the compound to deter predation. It is classified among the secondary metabolites.
The skeletal formula of the capsaicin molecule. Carbons and hydrogens may be omitted where implicit.
There are actually several capsaicinoids, which are present in different amounts in different species. This accounts for the delayed reaction to C. chinense (habanero) as compared to other species.
- trans-8-methyl N-vanillyl 6-nonenamide
- 8-methyl N-vanillyl nonamide
- 7-methyl N-vanillyl octamide
- 9-methyl N-vanillyl decamide
- trans-9-methyl N-vanillyl 7-decenamide
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Ointments and balms for the relief of aching muscles often contain capsaicin in the form of a chili oil extract, listed amongst the ingredients under such names as "capsic. oleo. res."
Uses
Food
Because of the burning sensation capsaicin is commonly used in food products to give them added spice or heat. The degree of heat found within a food is measured on the Scoville scale. Typically the capsaicin is obtained by using chili peppers as the source. Another common source is hot sauces (which may contain pure capsaicin or chili peppers). These sources are preferred over pure capsaicin for reasons of safety resulting from the lower concentration. Capsaicin is fat-soluble rather than water-soluble, so the drinking of water offers little relief from the burning sensation of excessively spiced food. Eating (unspiced) fatty food (buttered bread, ice-cream etc.) will extract the residual capsaicin from the mouth and relieve the burning.
Medical
Capsaicin is used in topical ointments used to relieve the pain of peripheral neuropathy (for example postherpetic neuralgia). The treatment typically involves the application of a topical anesthetic until the area is numb. Then the capsaicin is applied by a therapist wearing rubber gloves and a face mask. The capsaicin remains on the skin until the patient starts to feel the heat at which point it is promptly removed. The result appears to be that the nerves are overwhelmed from the burning sensation and are unable to report pain for an extended period of time. Non-Lethal Force
Capsaicin is also the active ingredient in the chemical riot control agent pepper spray. When the spray comes in contact with skin, especially eyes or mucous membranes it is very painful. Refer to the Scoville scale for a comparison of pepper spray to other sources of Capsaicin.
Mechanism of Action
The burning and painful sensations associated with capsaicin result from capsaicin's chemical interaction with sensory neurons. Capsaicin, as a member of the vanilloid family, binds to a receptor called the vanilloid receptor subtype 1 (VR1), which is a ion channel-type receptor. VR1, which can also be stimulated with heat and physical abrasion, permits positively-charged ions (i.e. cations) to pass through the cell membrane and into the cell from outside when activated. The resulting "depolarization" of the neuron stimulates it to signal the brain. By binding to the VR1 receptor, the capsaicin molecule produces the same effect that excessive heat or abrasive damage would cause, explaining why the spiciness of capsaicin is described as a burning sensation.
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