Why mint makes your mouth feel cold

HostYou know that startling rush when you chew a piece of mint gum and then take a cold sip of water? It feels like your mouth just turned into a block of ice. It's almost too much to handle. But if you actually put a thermometer in your mouth, the temperature hasn't changed at all. The water is just room temperature, yet it feels like it came out of a freezer.

HostSo, what's going on in our mouths that makes mint feel so icy when there's no actual ice involved?

GuestIt's all a big trick. Your mouth isn't actually getting colder. What's happening is that the mint is messing with the hardware your body uses to feel the world. We have these tiny sensors on our nerves that are built to tell us when things get chilly. Their whole job is to send a flash of electricity to your brain saying, hey, it's cold in here. Normally, they only turn on when the temperature drops. But mint contains a special oil called menthol. And menthol is shaped in a way that it can actually bump into those sensors and flip the switch, even if the room is perfectly warm.

HostSo the brain is just getting a fake message?

GuestThat's exactly it. Think of those sensors like little gates on the surface of your nerve cells. When it gets cold, the gate opens up and lets a signal through. But menthol is like a skeleton key. It happens to have just the right shape to slide into the lock and pull the gate open. Once that gate is open, your nerve starts firing. It tells your brain that things are freezing, even though the thermometer says everything is fine. Your brain has no way of knowing the difference between a drop in temperature and a chemical key opening that door. It just sees the signal and says, okay, we're cold now.

HostBut wait, if I'm not actually cold, why does it feel ten times worse when I drink water? If the menthol already flipped the switch, why does the water matter?

GuestThat's where it gets really interesting. Menthol does more than just flip the switch. It actually makes the sensor much more sensitive than usual. It lowers the bar for what counts as cold. So if your mouth is at its normal temperature, the menthol tricks the sensor into thinking that normal warmth is actually quite chilly. Then, when you take a sip of water that's even just slightly cool, the sensor goes into overdrive. It reacts as if you just swallowed liquid nitrogen. It's like the menthol turned up the volume on your cold sensors to the highest possible setting, so even a tiny breeze or a sip of water feels like a blizzard.

HostIt's strange that one little plant can hijack our nerves like that. Is this the same thing that happens with spicy food, just in the other direction?

GuestIt's a very similar trick. Hot peppers have a stuff in them called capsaicin. It does the same thing, but it targets the sensor that feels heat and pain. That's why we call peppers hot. They're not literally burning your tongue with fire, but they're flipping the switch that tells your brain, ouch, this is way too hot. It's funny because your body uses the same basic system for both, just different doors for different feelings. Mint is the cool version of that heat.

HostI have noticed that if the mint is really strong, like in some throat lozenges or intense gum, it stops feeling cool and starts to feel like it's actually stinging or burning. If it's supposed to be cold, why does it start to hurt?

GuestThat happens because your body has a few different types of these sensors. There's the one that just feels a nice chill, but then there are others that are only supposed to turn on when things are dangerously cold, like ice-burn territory. When you have a really high amount of menthol, it stops being picky. It starts jamming its way into those danger sensors too. When those fire, your brain stops thinking, oh, this is refreshing, and starts thinking, something is wrong. That's when you get that stinging or biting feeling. It's a sign that you have pushed the system a bit too far.

HostIt seems like a lot of work for a plant to go through. Why would a plant even want to trick us into thinking our mouths are freezing?

GuestWell, the plant isn't doing it for us. It's doing it to stay alive. To a small bug or a worm, that cooling feeling isn't a refreshing snack. It's an irritant. It's a way to tell things that might want to eat the plant to go away and find something else. Most animals in the wild take that stinging, weird feeling as a warning sign. Humans are just the odd ones out who decided we actually quite like the feeling of a fake winter storm in our mouths. We took a defense system and turned it into a flavor.

HostSo we're basically eating a warning sign and enjoying the confusion it causes in our nerves.

GuestWe really are. We have taken this chemical tool that plants use to scare off pests and we have put it in everything from toothpaste to ice cream. We have even started using it on our skin in those cooling creams for sore muscles. It's the same trick there too. It doesn't actually ice your muscles down, it just convinces your brain to focus on the cold signal instead of the pain signal. It's a beautiful bit of misdirection that we have learned to use to our advantage.

GuestEven though we have mapped out how that menthol key fits into the lock, our brains still fall for the trick every single time we chew a piece of gum.

HostThe mint plant is still winning the battle of wits, making us feel the ice of a winter day even while we sit in the summer sun.