The active ingredient in mint, menthol, binds to a protein in sensory neurons called TRPM8. TRPM8 is an ion channel that regulates the flow of ions among cellular membranes. When menthol binds to TRPM8, the ion channel opens and allows Na+2 and Ca+2 ions to enter the cell. These ions change the electric charge and alter the electric potential within the nerve cell, causing the brain to believe that it is cold inside the mouth.
There are some foods that are inherently hot, such as chili peppers. Take a hungry bite from a particularly ‘hot’ chili and you’ll probably spend the next ten minutes like this:
Then, on the other side of the spectrum, there are foods that are inherently ‘cold’, including mint. While we’ve already written a post about what makes chili peppers so hot, it’s time to investigate the other extremity of the taste spectrum.
No matter how hot the ambient air is, the moment you suck on a mint candy or chew on a stick of mint gum, the breath you draw feels pleasantly cool. Why is that?
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TRPM8: The Sentry Of Coldness!
This seemingly strange phenomenon is nothing but a trick that mint plays on your brain to make it feel like it’s cold outside.
The sensory neurons present in your skin and mouth contain a very important protein; it’s called “transient receptor potential cation channel subfamily M member 8” (or simply, TRPM8). This is not just another protein with a rather long name; in fact, it also plays a vital role in helping you feel sensations of coldness. To be more specific, biologically, it’s an ion channel and therefore regulates the flow of ions among cellular membranes.
Think of it this way: not all keys can open a lock; there are only so many keys that can click a lock open. Similarly, there are only a few chemicals that can unlock the ion channel and subsequently access the cell.
In this case, TRPM8 is an ion channel that opens up when it senses cold. It then allows Na+2 and Ca+2 ions to enter the cell. These ions change the electric charge and alter the electric potential within the nerve cell. Due to this, the electric signals reaching the brain are modified and the brain is led to believe that it’s cold inside the mouth, when in fact, there is no change whatsoever in the temperature inside the mouth!
Now, TRMP8 not only responds to cold temperatures, but also to the presence of certain stimulants. And what is that artificial stimulant that makes you feel cold inside your mouth, irrespective of the ambient temperature?
Menthol
Mint contains an organic compound known as menthol, which is commonly found in peppermint and other mint oils. Menthol binds to TRMP8, and subsequently, the ion channel opens up, as if the temperature inside the mouth had dropped. Your brain receives those ‘cold’ signals from the mouth due to the altered electric potential, so your breath feels cold. Precisely why menthol binds with TRMP8 is something that scientists still don’t know with absolute assurance; what they do know is that it does bind with TRMP8.
Even after you spit out the mint gum, the cold sensation lingers on for a bit before the ion channel becomes desensitized again and returns to its normal temperature.
So if you’re out exploring the endless expanse of a desert and the ambient air feels unbearably hot, you know what to do to make things ‘cool’!
Suggested Reading
Ignition!: An Informal History of Liquid Rocket Propellants (Rutgers University Press Classics)
