Tasteless, colourless, odourless and painful, pure capsaicin is a curious substance. It does no lasting damage, but the body's natural response to even a modest dose (such as that found in a chili pepper) is self-defence: sweat pours, the pulse quickens, the tongue flinches, tears may roll. But then something else kicks in: pain relief. The bloodstream floods with endorphins-the closest thing to morphine that the body produces. The result is a high. And the more capsaicin you ingest, the bigger and better it gets.

Which is why the diet in the rich world is heating up. Hot chilies, once the preserve of aficionados with exotic tastes for cuisine from places such as India, Thailand or Mexico, are now a staple ingredient in everything from ready meals to cocktails.

One reason is that globalisation has raised the rich world's tolerance to capsaicin. What may seem unbearably hot to those reared on the bland diets of Europe or the Anglosphere half a century ago is just a pleasantly spicy dish to their children and grandchildren, whose student years were spent scoffing cheap curries or nacho chips with salsa. Recipes in the past used to call for a cautious pinch of cayenne pepper. For today's guzzlers, even standard-strength Tabasco sauce, the world's best-selling chili-based condiment, may be too mild. The Louisiana-based firm now produces an extra-hot version, based on habanero peppers, the fieriest of the commonly-consumed chilies.

But for the real "heat geeks", even that is too tame. Tesco, Britain's biggest supermarket chain, recently added a new pepper to its vegetable shelves: the Dorset naga. Inhaling its vapour makes your nose tingle. Touching it is painful; cooks are advised to wear gloves. It is the only food product that Tesco will not sell to children. By the standards of other chilies, it is astronomically hot. On the commonly used Scoville scale (based on dilution in sugar syrup to the point that the capsaicin becomes no longer noticeable to the taster) it rates 1.6m units, close to the 2m score of pepper spray used in riot control. The pepper that previously counted as the world's hottest, the Bhut Jolokia grown by the Chile Pepper Institute at the New Mexico State University, scored just over 1m. That in turn displaced a chili grown by the Indian Defence Research Laboratory in Tezpur, which scored a mere 855,000. The hottest habanero chilies score a wimpy 577,000.

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