Pepper Spray is a hot topic in the news recently after it was used on passive OWS protestors in California. Hot peppers contain capsaicin, a chemical that binds to human nociceptors (pain receptors) producing a “spicy” hot or burning sensation at lower concentrations and pain at higher concentrations. The form that police use or is sold for self defense has many times the concentration of capsaicin found naturally in the hottest peppers.
Humans have only recently discovered the self-defense properties of capsaicin. Pepper plants have been using capsaicin for “self-defense” for millions of years. Pepper plants are not alone in using chemical defense. Many plant species are defended from herbivores and pathogens by producing toxic chemicals that the plants can tolerate but make the plants inedible to most animals. Human include only a tiny fraction of the hundreds of thousands of plant species on the planet in our diets. Most plants are either toxic (think deadly nightshade) or inedible (pine needles for instance). This is a consequence of plant defensive chemistry.
Capsaicin is a deterrent to feeding by many animals, including insects and mites. In the scientific literature, capsaicin is an oviposition deterrent for onion flies, and has insecticidal and miticidal properties. There is a patent for adding capsaicin to fruit wax as added protection against insect damage.
Capsaicin is popular among organic gardeners because as Megyn Kelly points out, “It’s a food product essentially.” Numerous recipes for are available from Sierra Club and other groups on “Insect Killing Sprays You Can Make in Your Own Kitchen”. Many of these sprays extract the capsaicin from hot peppers to be sprayed on everything from house plants to vegetables and foraging ants. National Geographic reminds us that capsaicin can be toxic to beneficial insects such as honey bees.
It is interesting that people appalled by police use of pepper spray tout the dangers and toxic effects on humans, while organic gardeners swear to its safety. After all, capsaicin is natural, it comes from a plant. How does one parse the truth about pepper spray?
The disconnect for the public comes from the dualistic notion that chemicals that are either toxic and harmful or non-toxic. The truth is far more nuanced. Paracelsus, considered “The Father of Toxicology”, studied poisons in the early 1500s Italy. Paracelsus observed that all chemicals can be poisons. It is the dose that makes the poison.
In the 21st century, “the dose makes the poison” should be conventional wisdom, but it isn’t. It is clear that small amounts of alcohol can enhance a meal, but large doses can make someone sick or kill them (alcohol poisoning). Table salt, commonly used to add flavor to foods, is well tolerated at moderate doses. However ingesting large amounts of table salt can be lethal. These simple examples point to the larger truth that small amounts of chemicals can be tolerated, but large enough amounts of any chemical (natural or synthetic) has the potential to cause harm. The key is the amount.
Capsaicin concentration is important in peppers and pepper spray. Small doses of capsaicin can have a deterrent effect on insects yet be relatively harmless to humans. However, if doses of capsaicin are high enough, it can cause adverse effects. Just because a chemical is found in nature, does not mean it is safe to use on people at very high doses. The amounts that home gardeners use in sprays produced from home grown peppers is far lower than the dose in pepper sprays for use in personal protection, to ward off bears or used for crowd control by police.
Another factor is the differing affects on different tissues. Cutting a hot pepper in the kitchen can coat fingers with capsaicin. A finger in the mouth will impart a spicy taste. However, rubbing the eyes with a capsaicin coated finger can be painful. Obviously, those using hot pepper spray for insect control should take precautions to prevent the spray from entering the eyes.
The dose of capsaicin tolerated can vary markedly among species. One species of caterpillar, Heliothis assulta, is one of the few herbivores capable of feeding on the fruits of hot peppers, Capsicum annuum. Heliothis assulta is more tolerant of capsaicin than other closely related species. The tolerance may be due to decreased sensitivity of nerves to capsaicin or better metabolism of capsaicin by Heliothis assulta.
Capsaicin is like most other chemicals. At appropriate doses it can be used as a flavoring in our food in the form of hot peppers or it can be made into a spray for insect control that is relatively harmless to large animals (mammals and birds). At higher concentrations, capsaicin is useful as a deterrent to bears and dogs. At very high concentrations, capsaicin can have adverse effects on humans.
Paracelsus was correct, “The dose makes the poison.” People should treat all chemicals with respect to the appropriate dose for each use rather than making unwise assumptions that chemicals are either safe or unsafe. Dose is the key factor.