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The Toxicity of Capsaicin

author image Sam Lupica
Sam Lupica began scientific writing in 2007, specializing in physiology, toxicology and reproductive biology. He teaches chemistry and biology, and has published several journal articles in "Aquaculture Research" as well as informational articles in online publications. Lupica is finishing a Ph.D. in medical science and has a Master of Science in physiology and pharmacology from the University of Toledo College of Medicine.
The Toxicity of Capsaicin
A wooden scoop in a bowl of red chili powder on a table with fresh chilis.

Capsaicin is a colorless and odorless compound found in chili peppers, which creates a burning sensation in any tissue that it contacts. Capsaicin is produced in the fleshy parts of the pepper and is used in topical ointments, creams, and dermal patches to relieve pain. It is also the active ingredient in pepper spray, as it is an irritant to the eyes and lungs. In large quantities, capsaicin is toxic, causing difficulty in breathing and leading to convulsions. The quantity needed to kill an adult makes the risk of accidental poisoning by consumption unlikely. However, several studies have linked capsaicin to neurological problems and even tumor formation.

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Effects of Capsaicin on Nerve Cells

Chronic exposure to capsaicin depletes neurons of transmitters leading to reduction in sensation and consequent alleviation of pain. In a January 2010 article published in the “Journal of Toxicology and Environmental Health,” researchers sought to determine whether capsaicin affected the development or function of neural cells of mice. They concluded that capsaicin reduced the number of newly generated cells of the hippocampus but did not significantly alter learning and memory performance, but found that higher concentrations had the ability to kill neural cells.

Capsaicin and Liver Damage

In a 4-week feeding study, documented in the January 2007 edition of the “International Journal of Toxicology,” red chilli, or Capsicum annuum, was added to the diet of groups of male mice at concentrations up to 10 percent of the feed and was found to be relatively nontoxic. However when the study was continued as an eight-week feeding study using rats, necrosis of liver cells and aggregation of white blood cells were observed at this same concentration. Additionally hemorrhage of the stomach was observed in some of the animals that died.

Embryological Effects

In May 2006, an article appearing in the “International Journal of Toxicology” described an experiment to investigate the effects of capsaicin on embryo/fetal development, “from implantation [of the fetus] to closure of the hard palate.” Researchers used a dermal patch to deliver the irritant to pregnant rats and observed delays in skeletal formation and “significant reductions in the average number of metatarsals and ossified hindlimb and forelimb phalanges.”

Cancer and Capsaicin

Further, a September 2010 study published in “Cancer Research” documented animal experiments revealing that capsaicin can act as a cancer causing compound. The researchers found that several growth factors are activated by the presence of capsaicin and led to tumor formation in mice.

Conflicting Studies

Chili pepper consumption may be a strong risk factor for gastric cancer in populations with high intakes of chili pepper; however, other studies did not find this association. Although tumor promotion of capsaicin has been demonstrated, so have opposite effects. Overall, studies suggest that capsaicin can be, at best, irritating at low concentrations and, at worst, carcinogenic at high concentrations.

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