The burning and painful sensations associated with capsaicin result from its chemical interaction with sensory neurons. Capsaicin, as a member of the vanilloid family, binds to a receptor called the vanilloid receptor subtype 1 (TRPV1). First cloned in 1997, TRPV1 is an ion channel-type receptor. TRPV1, which can also be stimulated with heat, protons and physical abrasion, permits cations to pass through the cell membrane when activated. The resulting depolarization of the neuron stimulates it to signal the brain. By binding to the TRPV1 receptor, the capsaicin molecule produces similar sensations to those of excessive heat or abrasive damage, explaining why the spiciness of capsaicin is described as a burning sensation.
Early research showed capsaicin to evoke a long-onset current in comparison to other chemical agonists, suggesting the involvement of a significant rate-limiting factor. Subsequent to this, the TRPV1 ion channel has been shown to be a member of the superfamily of TRP ion channels, and as such is now referred to as TRPV1. There are a number of different TRP ion channels that have been shown to be sensitive to different ranges of temperature and probably are responsible for our range of temperature sensation. Thus, capsaicin does not actually cause a chemical burn, or indeed any direct tissue damage at all, when chili peppers are the source of exposure. The inflammation resulting from exposure to capsaicin is believed to be the result of the body's reaction to nerve excitement. For example, the mode of action of capsaicin in inducing bronchoconstriction is thought to involve stimulation of C fibers culminating in the release of neuropeptides. In essence, the body inflames tissues as if it has undergone a burn or abrasion and the resulting inflammation can cause tissue damage in cases of extreme exposure, as is the case for many substances that cause the body to trigger an inflammatory response.
Acute Health Effects
Capsaicin is a strong irritant requiring proper protective goggles, respirators, and proper hazardous material-handling procedures. Capsaicin takes effect upon skin contact (irritant, sensitizer), eye contact (irritant), ingestion, and inhalation (lung irritant, lung sensitizer). LD50 in mice is 47.2 mg/kg.
Painful exposures to capsaicin-containing peppers are among the most common plant-related exposures presented to poison centers. They cause burning or stinging pain to the skin and, if ingested in large amounts by adults or small amounts by children, can produce nausea, vomiting, abdominal pain, and burning diarrhea. Eye exposure produces intense tearing, pain, conjunctivitis, and blepharospasm.
When used for weight loss in capsules, there has been a report of heart attack; this was thought to be due to excess sympathetic output.
Treatment After Exposure
The primary treatment is removal from exposure. Contaminated clothing should be removed and placed in airtight bags to prevent secondary exposure.
For external exposure, bathing the mucous membrane surfaces that have contacted capsaicin with oily compounds such as vegetable oil, paraffin oil, petroleum jelly (Vaseline), creams, or polyethylene glycol is the most effective way to attenuate the associated discomfort; since oil and capsaicin are both hydrophobic hydrocarbons the capsaicin that has not already been absorbed into tissues will be picked up into solution and easily removed. Capsaicin can also be washed off the skin using soap, shampoo, or other detergents. Plain water is ineffective at removing capsaicin, as are bleach, sodium met bisulfite and topical antacid suspensions. Capsaicin is soluble in alcohol, which can be used to clean contaminated items.
When capsaicin is ingested, cold milk is an effective way to relieve the burning sensation (due to caseins having a detergent effect on capsaicin; and room-temperature sugar solution (10%) at 20 °C (68 °F) is almost as effective. The burning sensation will slowly fade away over several hours if no actions are taken.
Capsaicin-induced asthma might be treated with oral antihistamines or corticosteroids.
Effects on Weight Loss and Regain