Nerves are the wiring of the brain, carrying information in the form of electric currents. Our nervous system is built to sense changes in temperatures – a whole set of nerves running from our skin to the brain is dedicated to conveying just that information. The receptor protein that senses the change in temperature is called TRPM8 and it is found in all cold-sensing nerve cells.
When the temperature in your mouth drops, TRPM8 changes its shape to allow calcium ions to flow into the nerve cell. That triggers a current that goes to the brain. That's what makes you feel the sensation of being cold.
But certain natural chemicals can activate TRPM8 on their own. One of them is menthol, which gives peppermint its pizzazz. According to Ghosh, TRPM8 was actually first discovered because it responded to menthol. It was only later that scientists found what's probably its original biological purpose, the reaction to temperature.
After all, your body has a reason to respond to super hot or super cold foods, but not much reason to freak out over mint consumption.
Because menthol and capsaicin both activate your skin's temperature sensors, they can make you feel numb. So in addition to giving us another flavor dimension to work with, this biological quirk also provides a great source for topical painkillers.