Why Does Mint Feel Cold? - Science Notes

Have you ever wondered why mint feels cold when you eat it, inhale it, or apply it to your skin? The cooling sensation is due to a trick of brain chemistry. Here’s how it works.

Why Mint Feels Cold

Cold temperatures change the shape of a protein called transient receptor potential cation channel subfamily M member 8 (TRPM8). This protein occurs in nerve cells in the skin and taste buds. The shape change opens a channel, allowing sodium (Na+) and calcium (Ca2+) ions to flow into the nerve cell. The ions change the electrical charge of the neuron and fire a signal to the brain. The brain interprets the signal as a cold sensation.

An organic compound called menthol in mint binds to TRPM8 and changes the shape of the protein. The ion channels open and the neurons fire the same signal as if they were exposed to cold. The difference is that menthol doesn’t immediately un-bind from TRPM8. It sensitizes neurons so the cold effect doesn’t immediately wear off. If you sip cold water after chewing a breath mint or spitting out mint-flavored toothpaste, the water feels especially cold.

Menthol isn’t the only chemical that binds TRPM8 and causes a cold sensation. Thymol, sugar alcohols, and many pesticides produce the same effect. While scientists don’t know for certain, it’s likely plants make these chemicals as natural antimicrobial agents and pest deterrents.

Why Hot Peppers Feel Hot

The capsaicin in hot peppers feels hot because capsaicin binds to the TRP-VR1 receptor. Normally, heat changes the conformation of TRP-VR1, sending a signal to the brain indicating a warm temperature. When capsaicin binds to the receptor, the signal for heat gets sent without the temperature change. In fact, the signal from capsaicin is so strong that cold water laced with hot peppers feels hot!

What About Mixing Mint and Hot Peppers?

So, you might wonder what happens if you put the menthol from mint and the capsaicin from hot peppers together. Initial research indicates that eating mint reduces the burn from hot peppers, but only if you eat the mint first and immediately follow it with the hot pepper. Eating mint after you feel the burn probably doesn’t help. However, you can test the effect for yourself using the scientific method. Be sure to recruit a lot of friends to test what happens when you mix mint and hot peppers so you have a lot of data!

Menthol from mint and capsaicin from hot peppers occur together in many topical pain relief remedies. When applied to skin, the effect is both icy and hot. Exposure to menthol and capsaicin has a numbing effect, plus both chemicals increase skin circulation.

References

• Amano, A. (1986) “Cooling and pungent agents”. J. Jap. Soc. Cut. Health 17: 77–86.
• Atkinson, R. W.; Yoshida, H. (1882). “On peppermint camphor (menthol) and some of its derivatives”. J. Chem. Soc., Trans. 41: 49. doi:10.1039/CT8824100049
• Duke, James A. (2002). “Peppermint”. Handbook of Medicinal Herbs (2nd ed.). ISBN 978-0-8493-1284-7.
• Eccles, R. (1994). “Menthol and Related Cooling Compounds”. J. Pharm. Pharmacol. 46 (8): 618–630. doi:10.1111/j.2042-7158.1994.tb03871.x
• Turner, E. E.; Harris, M. M. (1952). Organic Chemistry. London: Longmans, Green & Co.

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