Why do mints make your mouth feel cold?

Cambridge University's Sarah Madden took on Alan's cool question...

Sarah - It’s a very good question. The reason is that mints contain something called menthol and I have some mints with me here. Basically what happens is that the menthol in the mints hits a cold receptor that we have in our mouth. Obviously this receptor would normally be sensitive to temperature.

Chris - When you say cold receptor - what’s that?

Sarah - It’s a protein, so a unit in our mouth. It’s actually in the membrane; it’s like a channel. So what happens is sodium and calcium ions can go between it and this affects our nerves…

Chris - So it’s our nerve cells in your mouth?

Sarah - Yes. It affects nerve cells and then sends signals to our brain. So, basically, we eat menthol and this attaches to this receptor, and this sends a signal to our brain tricking us, making us think that our mouth is cold. Whereas, in fact, it’s just the menthol.

Chris - So, you’ve got cold sensing nerve fibres in your mouth. Now the opposite, of course, must be the chilli reaction isn’t it? Because I love curry and I’m very fond of the burn you get with a chilli and that’s where things feel artificially a lot hotter?

Sarah - That’s actually working by a very similar process. We have a different receptor, which is actually very similar to the mint one, and there’s a chemical in chillies called capsaicin. So what happens is again, that compound hits the receptor fooling your brain into thinking your mouth is on fire.

Chris - It certainly does, yeah.

Sarah - We were curious as to whether the two could cancel each other out? Because often you have mint yogurt when you have curry, for example, to try and cool them down.

Chris - Ohh what a good idea.

Sarah - I actually did some research into this.

Chris - Can we do the experiment. I notice you’ve brought some apparatus with you, which is a bag of menthol mints and you‘ve also got - what on earth is that?  Is that a bag of of chillies?

Sarah - Yes, that’s right.

Chris - OK. I volunteer Philipe  - no I’m just kidding. We should all do it. In the interests of having a good number of research participants, we should all have a go shouldn’t we?

Philipe - I’d just like to say, in the interest of science, this would be a bad decision - I’m just saying!

Chris - So what’s the experiment we’re going to try?

Sarah - We’ve done research in humans and mice to see if they counteract each other. Because, obviously, this is an illusion that’s happening in your mouth. It’s tricking your brain. They put these chemicals in the rat’s milk to see if they would have less or more.

Chris - So a mixture of menthol plus chilli to see if the hot effect makes the cold effect go away?

Sarah - Yeah. And, actually, it seems that it does.

Chris - Shall we find out?

Sarah - So, we’re going to see if it works on us as well.

Chris - Did you know that you guys that when you came in you were going to be doing this? She’s got a bag of raw chillies here. Do you like chilli Andrew?

Andrew - Not raw chilli. I think I might just hide at this point. Am I allowed to hide?

Chris - There’s chunks of whole chilli coming…

Andrew - With the seeds as well which are particularly bad, aren’t they?

Chris - I’ve got to do this as well.

Sarah - If you want to. And I’ve got some mints as well that you can pass around.

Chris - Here comes the mints. Are they maybe necessary?

Andrew - We’ve actually got giant chunks as well. Do we have to eat all of this?

Sarah - I'm not enforcing the entire chunk.

Chris - Sarah; this is a lot of chilli! This is a massive…

Andrew - We’ll not be able to speak for the remaining half an hour.

Sarah - The way it’s been proven in this paper, we should be very scientific. So we have to have the mint first because it’s been proven that it produces the cooling.

Chris - I’m eating the mint.

Andrew - Hang on a second. There’s no control sample here.

Chris - Just eat your mint and behave. Right, we’ve all chewed the mint… now what?

Sarah - You should be noticing our mouth is feeling slightly colder because of the menthol.

Chris - They taste nice. These are quite nice, I might get some more of these.

Sarah - Yeah. I’ve got the best for you guys you know.

Chris - They’re not good for your teeth though; it’s pure sugar I think.

Sarah - Now if we have the chilli. Having as much as you like.

Andrew - This is huge! Have I got to eat all of that?

Sarah - That’s extremely hot!

Andrew - Oh wow!

Chris - I eat very hot curries. But i’ve just eaten the whole thing and that’s quite hot.

Sarah - It’s much hotter than I thought it would be. We can see that it has actually reduced the coolness. Maybe slightly overpowered the coolness!

Chris - I think that’s just everyone losing consciousness, Sarah. I think we can say it doesn’t work on the basis of my personal…

Sarah - So the cold feeling is still…

Chris - It’s not working. My mouth is burning.

Sarah - But what it’s meant to do; it’s meant to reduce the cold effect. It doesn’t mean that it’s going to get…

Andrew - I did say that we didn’t have a control sample. We don’t know whether it works or not.