Think back to the last time you sucked on a peppermint candy. The red-and-white striped treat instantly made your mouth feel cool. Though people have enjoyed peppermint for thousands of years, it wasn’t until recently that scientists figured out why it makes us feel chilly.
Peppermint extract—made from the plant’s oils—are added to candy.
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Cool Trick
Scientists have discovered how a compound in peppermint makes us feel cold
PEPPERMINT: UNWRAPPED
Peppermint is a type of plant that’s grown throughout the world. Scientists have long known that this small, leafy herb contains the chemical menthol, which gives peppermint its cooling sensation. But menthol doesn’t actually make your body temperature drop. It just tricks your brain into thinking you’re experiencing cold.
David McKemy, a neurobiologist at the University of Southern California, has discovered exactly how menthol deceives the brain. He researches thermosensation, the science behind how the human body senses heat and cold.
McKemy discovered that a protein called TRPM8 sends a signal to our brain when we feel something cold. But the protein doesn’t respond only to chilly temperatures: Menthol also causes it to send a “cold” signal.
Menthol molecules attach to the TRPM8 protein found on nerve cells and tell the protein to send a cold signal to the brain (see How Menthol Fools You Into Feeling Cold). This results in the chill you feel while eating a candy cane, chewing gum, or gargling mouthwash.
OTHER PLANT PRANKS
Menthol isn’t the only chemical that plays tricks on us. A chemical in hot peppers called capsaicin can fool us into feeling hot. Like menthol, capsaicin attaches to a protein called TRPV1, causing it to send a “hot” signal to the brain. That’s why eating spicy peppers can create a burning sensation and make you sweat.
“It’s like menthol and capsaicin shift the thermostat of your cells,” says McKemy. “They cause the TRPM8 and TRPV1 proteins to respond at room temperature—without the presence of cold or heat."
MINTY MEDICATION
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Oils in peppermint leaves contain menthol.
McKemy is interested in how we sense temperature because it could have important implications for people’s health. “If we understand how the body perceives pain when something is too hot or too cold, we can then use that information to treat painful conditions like burns or frostbite,” he says.
Menthol can also act as a medication to treat certain injuries. For example, if you strain a muscle, you’ll likely experience painful inflammation and swelling as the wound heals. Putting a cold ice pack on the sore spot can reduce inflammation. Similarly, applying menthol-rich lotions like IcyHot tricks the body into feeling cold, which counteracts the effects of inflammation.
But medicines like IcyHot are used to treat only mild pain. Lab studies have shown that menthol administered intravenously (directly into the bloodstream) can also reduce pain due to inflammation throughout the body. Scientists hope that this research could lead to the creation of more-powerful medications to relieve severe pain caused by chronic diseases such as cancer or traumatic injuries.
“It’s not clear why the peppermint plant evolved this unique adaptation,” says McKemy, “but it’s amazing how our bodies react to its properties.”
CORE QUESTION: Why does peppermint make people feel cold? Explain in your own words.
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