Lauren Collins in The New Yorker:
“Chili pepper” is a confusing term, another of Christopher Columbus’s deathless misnomers. (Columbus and his men classified the spicy plant they had heard being referred to in Hispaniola as aji—farther north, in Mexico, it was known by the Nahuatl word chilli—as a relative of black pepper.) Chilis belong to Capsicum, a genus of the nightshade family. Horticulturists consider them fruits, and grocers stock them near the limes and cilantro. Most chilis contain capsaicin, an alkaloid compound that binds to pain receptors on the tongue, producing a sensation of burning. Sweet banana peppers are usually neutral. Pepperoncini (approximately 300 SHU) produce just a flicker of heat, while cayennes (40,000) are to Scotch bonnets (200,000) as matches are to blowtorches. Capsaicin is meant to deter predators, but for humans it can be too little of a bad thing. Because capsaicin causes the body to release endorphins, acting as a sort of neural fire hose, many people experience chilis as the ideal fulcrum of pain and pleasure.
In recent years, “superhots”—chilis that score above 500,000 on the Scoville scale—have consumed the attention of chiliheads, who debate grow lights on Facebook (“You can overwinter with a few well-placed T-8s”), swap seeds in flat-rate boxes (Australian customs is their nemesis), and show up in droves at fiery-foods events (wares range from Kiss My Bhut hot sauce to Vanilla Heat coffee creamer). Chilis, in general, are beautiful. There is a reason no one makes Christmas lights in the shape of rutabagas. Superhots come in the brightest colors and the craziest shapes.