Chili pepper

An herbaceous plant to small shrub, 0.5–1.5 m tall and much-branched, with a smooth or slightly hairy stem. Leaves are simple and alternate, ovate to pointed, with entire margins. Flowers are small and star-shaped with five lobes, white or slightly purple, borne singly in the leaf axils and largely self-pollinating. The fruit is a hollow berry (two to four locules), green when unripe and turning red, yellow, orange or purple at maturity, 2–30 cm long by cultivar, with a white central core bearing many flat cream-yellow seeds. Roots are shallow and occupy the topsoil.

According to Plants of the World Online (Kew), Capsicum annuum L. has a native range from "S. U.S.A. to Brazil, Caribbean" — an annual, subshrub or shrub of seasonally dry tropical habitats; the typical variety (var. annuum) originates from central Mexico. Chili was domesticated in Mexico about 6,000 years ago, one of the oldest crops of the Americas, and after the 15th century Europeans carried it to Asia, Africa and the rest of the world. Today it is grown everywhere, with China, India, Türkiye and Mexico among the largest producers.

The characteristic pungency comes from capsaicinoids, chiefly capsaicin (C18H27NO3) and dihydrocapsaicin — fatty-acid amides that selectively activate the TRPV1 ion channel on sensory nerve endings, producing a burning sensation followed by desensitisation. Capsaicin was first purified in 1876 and its structure described in 1919; pungency is measured on the Scoville scale (SHU), pure capsaicin corresponding to about 16 million SHU. Ripe fruit is also rich in vitamin C (higher than orange by weight), provitamin A (beta-carotene), the red carotenoid pigments capsanthin and capsorubin, and flavonoids and minerals (potassium, iron, magnesium).

On uses and research, chili is a staple spice: fresh fruit, powder, sauce and paste, and sweet bell peppers used as a vegetable. Medically, topical capsaicin products — 0.025–0.1% creams in common use since the early 1980s and the high-concentration 8% patch — are indicated for post-herpetic neuralgia (PHN) and diabetic peripheral neuropathy (DPN); clinical studies typically applying three to five times daily for 2–6 weeks show modest pain relief, and the 8% patch achieved about a 30% reduction in NPRS pain scores with a median response of about 22 weeks. Reviews published in 2024 (Zhang et al.; Heliyon) confirm capsaicin's antioxidant, anti-inflammatory and anticancer effects and its potential in obesity control and cardiovascular health — though more research is needed.

On safety, capsaicin and hot peppers can cause burning and irritation of skin and mucous membranes (especially the eyes), so wash hands after handling and avoid applying to broken skin; eating too much hot pepper may cause stomach burning, heartburn, diarrhoea or irritation of haemorrhoids, and people with irritable bowel syndrome should limit intake. Sweet peppers are generally safe and nutritious. On conservation, Capsicum annuum is assessed as Least Concern (LC) by the IUCN — the assessment of Aguilar-Meléndez et al. (2019, amended 2020, ID e.T100895534A172969027); the crop is not threatened, but landrace diversity and wild chili relatives need genetic conservation.