You can taste the cool, fresh flavor of mint for the same reason you feel pain.
Flavors like mint have long been associated with coolness, no matter what temperature they were served at. This is because mint is a natural source of the compound known as menthol. Synthesized and natural menthol has been added to drinks and cigarettes, as well as to creams and pads to produce a cooling sensation. It does this by binding to the aptly-named menthol receptor TRPM8 in the body's cells.
To test the exact function of TRPM8, scientists engineered TRPM8-less mice by removing the gene that codes for the menthol receptor.
When put in environments that offered them a choice between warm surfaces and cool ones, receptorless mice showed no particular preference, while regular mice skittered over to the warm side. The menthol receptor doesn't completely control temperature sensitivity. Once a certain surface was brought down to 10 degrees Celsius or below, even most of the modified mice moved away from it. Still, the lack of menthol receptors did knock out mild sensitivity and unpleasant sensations in the mice.
Menthol is used as more than just a way to put some refreshing kick into tea. It's also a natural analgesic. The cooling sensation numbs the area it touches. This numbing is why menthol is used for cough drops and creams for sore muscles. It's also why it's put in cigarettes - the menthol in the cigarettes numbs the throat to irritation from smoke. The revelation that menthol really does stimulate the receptors that control temperature response - and doesn't just provide a psychosomatic sensation of coolness - is important for scientists. Many medications that treat pain and irritation do so in the brain. This leads to serious side effects, and diminished mental accuity. Finding a way to numb people at receptors that first feel pain could take many of mental and physical side effects out of pain medication.
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