Cinnamon is the dried inner bark of trees of the genus Cinnamomum. These trees grow in Southeast Asia and India. The spice contains cinnamaldehyde. When you eat cinnamon-flavored foods, this compound activates your trigeminal nerve. This nerve supplies feeling in your face, nose, and mouth. “Cinnamaldehyde tricks you into thinking that your mouth is physically hot by setting off the same nervous system signals [as warmth],” says Terry Miesle, a flavorist in Illinois. Chili peppers have a similar effect, but with quick, fiery heat. Instead, “cinnamon gives you a nice warm feeling for a long time,” he says.