That seems to contradict common sense, which suggests that hot food causes an upset stomach-or what medical specialists call "gastric mucosal injury". A study in 1987 on the effects of ordinary pepper produced some signs of gastric exfoliation (stripping away the stomach lining) and some bleeding-though the effects were less than those produced by aspirin. An alarming-sounding experiment a year later involved volunteers being fed minced jalapeño peppers through a tube, directly into the stomach. The results, observed by an endoscope (a camera on a tube) revealed no damage to the mucous membrane. Against that is a study of heavy chili-eaters in Mexico City, who appeared to have higher stomach cancer rates than a control group. But the rate of illness had no correlation with the frequency of chilies eaten, leading to speculation that other factors may be at work.

Humans are the only mammals to eat chilies. Other species apparently reckon that nasty tastes are a powerful evolutionary signal that something may be poisonous. Paul Rosin, a psychology professor at the University of Pennsylvania, who is one of the world's best-known authorities on the effects of capsaicin, has had no success in persuading rats to eat chilies, and very limited success with dogs and chimpanzees: the handful of cases where these animals did eat chilies seemed to be because of their strong relationships with human handlers.

That offers a clue to the way in which mankind comes to develop a chili habit. In the same way as young people may come to like alcohol, tobacco and coffee (all of which initially taste nasty, but deliver a pleasurable chemical kick), chili-eating normally starts off as a social habit, bolstered by what Mr Rozin calls "benign masochism": doing something painful and seemingly dangerous, in the knowledge that it won't do any permanent harm. The adrenalin kick plus the natural opiates form an unbeatable combination for thrill-seekers. Just don't get it in your eyes.

... contd.