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That tingling, hot feeling usually comes from chili peppers, but sometimes from horseradish (a root) or mustard. Let’s talk about peppers. Their seeds have capsaicin (cap-SAY-uh-sin), which is an irritant to us. We feel this irritation like a burn. 

Pepper plants are trying to protect themselves—and make more pepper plants. Peppers are the juicy fruit of a flowering plant. Birds and animals eat the peppers and then poop out the seeds. That’s good! The seeds then grow in a new place. But when bugs eat the peppers, they leave little holes in the fruit. Tiny creatures called fungi (FUN-guy) enter the holes and eat the seeds, stopping them from growing. Capsaicin protects the seeds from the fungi. 

A lot of people think a little burn makes food taste better. But a lot of others don’t. Eating food that’s too spicy for you can hurt your mouth and your stomach. So it’s important to know your peppers before you eat. The Scoville Scale orders chili peppers from hottest to mildest. The hottest peppers can be more than 2 million times spicier than the mildest. Now that’s hot! 

To learn more, listen to NPR's interview with the biologist who discovered the connection between pepper heat and fungi.