That bowl of four-alarm chili is waging chemical warfare on your tongue. Chili peppers contain capsaicin (pronounced cap-SAY-ah-sin), a substance that triggers the sensations of pain and heat when it touches your tongue (or, in the case of the hottest peppers, even your hands). Pepper plants likely evolved this compound to keep away nibbling animals. Spicy-food connoisseurs build up a resistance to capsaicin by gradually eating progressively hotter peppers until they can nibble thermonuclear meals while working up only a mild sweat.
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