Plants That Kill: Capsaicin

Adapted from pages 122-123 of Plants That Kill:

The fruit and seeds of species of chilli peppers (Capsicum spp.) in the potato family (Solanaceae) contain a pungent compound, capsaicin, that makes food ‘hot’. As well as being used by humans as a spice for thousands of years, capsaicin also has medicinal applications, and the burning discomfort and pain it causes have found roles in riot-control and self-defence. 

The chilli or chili pepper (Capsicum annuum) is a small shrub from Mexico and Guatemala, with simple leaves and pendant, star-shaped flowers that appear singly and are followed by elongated, brightly coloured fruit. Numerous cultivars have been bred that vary in the size, shape and pungency of these fruit. They include the large, sweet bell peppers, as well as mild to hot chilli peppers. The taxonomy of chillies is complicated, however, with some cultivars of C. annuum having characteristics that overlap with those of two other species, the Tabasco pepper (C. frutescens) from Bolivia and western Brazil, and the very hot bonnet pepper (C. chinense), which despite its specific epithet is from Bolivia, northern Brazil and Peru. Some prefer to treat these three species and their cultivars as the ‘annuum–chinense– frutescens complex’. 

To alleviate the ‘heat sensation’ from chilli, try eating a yogurt raita containing chopped mint (Mentha spp.) leaves, as the menthol from the mint stimulates ‘cold sensation’ neurons. Photo credit: one photo, Shutterstock

Some culinary traditions use more chilli pepper than others, with the highest number being eaten in the species’ native Mexico (one chilli per person per day). Chilli has also been embraced in many of the countries to which it has been introduced, particularly India, where it is a key ingredient in curries, and Thailand. Either the fresh fruit and seeds, or the powdered or flaked dried fruit, are used for seasoning during cooking or as a condiment. 

The pungent compounds in chilli peppers, including capsaicin (8-methyl-N-vanilloyl-6-nonenamide), are capsaicinoid alkaloids, which bind to vanilloid receptors on sensory neurons (known as transient receptor potential vanilloid (TRPV) channels). These same receptors can also be stimulated by heat and pain, so the binding of the capsaicin results in the sensation of heat. The degree of burning and reddening is related to the concentration of capsaicinoids (see box) and duration of exposure (a dose-related response). TRPV channels are common to all mammals, and thereby deter rodents and other mammalian pests from eating chilli crops. Birds lack the capsaicin-binding site of these channels, however, so eat the ripe red fruit and disperse the seeds without harm. 

In addition to the sensation of heat and burning in the mouth, eating large amounts of hot chillies can cause irritation of the gastrointestinal tract. It is the burning discomfort and pain that chillies or concentrated chilli extracts cause to the eyes and nose that can be most distressing. Pepper sprays have proved to be effective weapons since they were first employed by Mayan Indians, and police forces in a number of countries now use them in the control of unruly individuals and crowds. However, the legality of using pepper sprays for self-defence varies around the world. 

Plants That Kill: A Natural History of the World’s Most Poisonous Plants
By Elizabeth A. Dauncey & Sonny Larsson

This richly illustrated book provides an in-depth natural history of the most poisonous plants on earth, covering everything from the lethal effects of hemlock and deadly nightshade to the uses of such plants in medicine, ritual, and chemical warfare.

Featuring hundreds of color photos and diagrams throughout, Plants That Kill explains how certain plants evolved toxicity to deter herbivores and other threats and sheds light on their physiology and the biochemistry involved in the production of their toxins. It discusses the interactions of poisonous plants with other organisms–particularly humans—and explores the various ways plant toxins can target the normal functioning of bodily systems in mammals, from the effects of wolfsbane on the heart to toxins that cause a skin reaction when combined with the sun’s rays. This intriguing book also looks at plants that can harm you only if your exposure to them is prolonged, the ethnobotany of poisons throughout human history, and much more.

A must for experts and armchair botanists alike, Plants That Kill is the essential illustrated compendium to these deadly and intriguing plants.

  • Provides an authoritative natural history of the most poisonous plants on earth
  • Features hundreds of color illustrations throughout
  • Looks at how and why plants produce toxins
  • Describes the effects of numerous poisonous plants, from hemlock and deadly nightshade to poppies and tobacco
  • Explains poisonous plants’ evolution, survival strategies, physiology, and biochemistry
  • Discusses the uses of poisonous plants in medicine, rituals, warfare, and more


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