英語時差：辣椒為什么那么辣？（上）

Bite into a hot pepper and it feels a lot like you’ve taken a sip of a hot drink. How can something that’s not hot in temperature produce the same reactions as something that is hot? Reactions like pain or sweating? It’s because although nerves in the skin can respond to different kinds of stimulation, such as pain, cold, and heat, they can also respond to chemicals. But chemical stimulation sends confusing signals to the brain. The chemical in chili peppers that makes them hot is called capsaicin. If capsaicin were to excite the pain receptors alone that might tell the brain you are being exposed to a dangerous extreme temperature. But in ways that aren’t completely understood, capsaicin stimulates both the temperature and pain receptors. That is, it simultaneously tells the brain that you are experiencing a modest increase in temperature as well as pain.