# How come the mouth is so insensitive to heat? **URL:** \ **Category:** Factual Questions\ **Created:** [December 11, 2006, 12:15am UTC](https://boards.straightdope.com/t/how-come-the-mouth-is-so-insensitive-to-heat/383621 "2006-12-11T00:15:06Z")\ **Posts on this page:** 9\ **Page:** 2
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [December 11, 2006, 8:09pm UTC](https://boards.straightdope.com/t/how-come-the-mouth-is-so-insensitive-to-heat/383621/21 "2006-12-11T20:09:59Z")
A couple of other weird things that I thought of after hitting submit: First is what CookingWithGas mentioned, put one hand somewhere hot and another hand somewhere cold then stick them in the same water and they both feel like different temperatures. The human body is good at detecting changes in temperature, but really sucks at detecting absolute temperature. Another weird thing is that if you take your handy dandy temperature probe and make it vary 25 deg C for 2 sec, 40 deg for 2 sec, 25 deg C for 2 sec, 40 deg C for 2 sec, etc. what your brain feels is 25 deg, 40 deg, 26 deg, 41 deg, 27 deg, 42 deg, i.e. it feels like it’s getting hotter overall when it isn’t. This is due to some weird integrative effect that occurs in the nerves, long before your brain even gets a chance to process the data. The last thing I wanted to mention is that if you play around with hot stuff a lot (like you work in a neurobiology lab and test machines out on yourself a lot) your pain threshold goes up a couple of degrees after a while. But, no matter how long you’ve been working there, 46 deg C feels awful F-ing hot. I don’t think you can say the hot coffee thing is just your mouth getting used to the temperature. ---
**Author:** ![bump](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bump](https://boards.straightdope.com/u/bump)\ **Post date:** [December 11, 2006, 10:09pm UTC](https://boards.straightdope.com/t/how-come-the-mouth-is-so-insensitive-to-heat/383621/22 "2006-12-11T22:09:02Z")
[QUOTE=engineer\_comp\_geek] I really don’t know why humans can tolerate coffee or tea that is 45 deg C. I’m wondering if it’s more of a simple thermodynamics thing instead of a chemical thing. Your mouth is full of saliva, etc. and the blood vessels are very close to the surface, so they could probably carry the heat away a lot quicker than they can in the skin of your arm. It could be that the skin inside your mouth isn’t heating up as quickly as the skin on your fingers as you are holding the coffee cup, for example. Just a WAG though. [/QUOTE] That was my first guess as well. I suspect that it’s probably the case, along with the thought that your hands may have thicker skin than other parts of your bodies- think about showering or bathing; it’s easy to get the water hot enough to make your crotch uncomfortable, but a lot harder to make your hands uncomfortable. ---
**Author:** ![Bippy\_the\_Beardless](https://avatars.discourse-cdn.com/v4/letter/b/ac8455/32.png) [@Bippy\_the\_Beardless](https://boards.straightdope.com/u/Bippy_the_Beardless)\ **Post date:** [December 11, 2006, 10:27pm UTC](https://boards.straightdope.com/t/how-come-the-mouth-is-so-insensitive-to-heat/383621/23 "2006-12-11T22:27:17Z")
Just a related question, but at what sort of temperature does real harm start to occur to skin cells? 47deg C may feel hot to everyone, but is damage occuring at that temperature? Do animals also have the ability to drink hot liquids in the way that Humans do, without pain even whne the liquid is too hot to happily touch with a finger. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [December 12, 2006, 2:44am UTC](https://boards.straightdope.com/t/how-come-the-mouth-is-so-insensitive-to-heat/383621/24 "2006-12-12T02:44:14Z")
[QUOTE=Bippy the Beardless] Just a related question, but at what sort of temperature does real harm start to occur to skin cells? 47deg C may feel hot to everyone, but is damage occuring at that temperature? [/QUOTE] The machines I designed had a safety cutoff circuit that triggered at 50 deg C, because I was told that above this temperature the skin would get damaged. 47 isn’t exactly what I would call pleasant, but it doesn’t damage the skin. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [December 12, 2006, 4:39am UTC](https://boards.straightdope.com/t/how-come-the-mouth-is-so-insensitive-to-heat/383621/25 "2006-12-12T04:39:08Z")
> [@](#): > > Many years ago, I designed a bunch of equipment for a neurobiologist who was studying pain. Just curious, did you happen to build a Machine which sucks out years of the subject’s life? ---
**Author:** ![Hostile\_Dialect](https://avatars.discourse-cdn.com/v4/letter/h/e495f1/32.png) [@Hostile\_Dialect](https://boards.straightdope.com/u/Hostile_Dialect)\ **Post date:** [December 12, 2006, 9:41am UTC](https://boards.straightdope.com/t/how-come-the-mouth-is-so-insensitive-to-heat/383621/26 "2006-12-12T09:41:03Z")
> [@rocksolid](#): > > And lips too, i mean they don’t seem like the hardiest of things yet they seem to survive a lot. Ever burned your lips at a party? That shit hurts. > [@rocksolid](#): > > i just assumed that if you boil a kettle and pour straight away there can’t be that much of a temperature drop. Considering all the super-hot water passing through it, the kettle (a) is very hot and (b) probably has a lot of steam trapped in it, especially if you’re talking about a hot water kettle for tea. When the coffee/water reaches equilibrium with the pot/kettle, both are at a pretty high temp. Your cup, on the other hand, is probably at room temperature, and (if I’m recalling my first-semester thermodynamics correctly) the first thing the coffee does upon arrival is transfer heat to the cup until the coffee and (the inside of) the cup are at the same temperature. Which means of course that the coffee cools down and the cup warms up. Not to mention that the coffee gets exposed to room temperature air on its way from the pot to the cup, and probably cools down to some extent at that point too. Am I getting this all right, physicists? > [@drachillix](#): > > Spicy on the other hand I can handle no problem. I always thought the Spanish “picante” (closer to “prickly”) was a better word for spicy than the English “hot”. Just a case of different cultures constructing different analogies, I guess, but prickling is a lot closer to what it actually does than burning. > [@Bippy the Beardless](#): > > Consider a hot cup of coffee or tea, it is often painful to hold the cup directly, that is why most cups have handles. Dispite this it is easy enough to drink the liquid therein. Don’t you sip the first few “hits” slowly and carefully, drawing it out to a wide surface area with a slow flow rate? Isn’t that an adaptive routine similar to holding the cup by its handle? I don’t see how this differentiates the hand from the mouth in heat sensitivity. Trickling a wide stream of coffee onto your hand slowly would surely hurt/burn less than quickly pouring a narrow stream of coffee onto your hand. ---
**Author:** ![Bippy\_the\_Beardless](https://avatars.discourse-cdn.com/v4/letter/b/ac8455/32.png) [@Bippy\_the\_Beardless](https://boards.straightdope.com/u/Bippy_the_Beardless)\ **Post date:** [December 12, 2006, 7:31pm UTC](https://boards.straightdope.com/t/how-come-the-mouth-is-so-insensitive-to-heat/383621/27 "2006-12-12T19:31:11Z")
[QUOTE=fetus] Don’t you sip the first few “hits” slowly and carefully, drawing it out to a wide surface area with a slow flow rate? Isn’t that an adaptive routine similar to holding the cup by its handle? I don’t see how this differentiates the hand from the mouth in heat sensitivity. Trickling a wide stream of coffee onto your hand slowly would surely hurt/burn less than quickly pouring a narrow stream of coffee onto your hand. [/QUOTE] Even after the coffee has cooled down anough to gulp, it still hurts to put your finger in the coffee. Similarly something too cold to hold comfortably can be plesant to eat (until you get brain freeze, that is). The mosture covering the inside of a mouth probably helps, but I’m not sure that is enough to account for the difference in heat/cold tollerance that seems to exist between mouth and hand. ---
**Author:** ![mlees](https://avatars.discourse-cdn.com/v4/letter/m/ba8739/32.png) [@mlees](https://boards.straightdope.com/u/mlees)\ **Post date:** [December 12, 2006, 7:38pm UTC](https://boards.straightdope.com/t/how-come-the-mouth-is-so-insensitive-to-heat/383621/28 "2006-12-12T19:38:38Z")
Hmm. Generally, the inside of my mouth has a coating of saliva in it. This may help protect the insides a little bit while drinking or eating hot stuff. I _think_ my lips are more sensitive to hot coffee than my tongue is, anyway. 🙂 But when I scald my tongue, it ends up feeling “fuzzy” (after I stop dancing around). Why is that? Is it becuase there are some dead nerves making my sense of taste and touch uneven/odd? ---
**Author:** ![Cheesesteak](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cheesesteak/32/3694_2.png) [@Cheesesteak](https://boards.straightdope.com/u/Cheesesteak)\ **Post date:** [December 12, 2006, 8:11pm UTC](https://boards.straightdope.com/t/how-come-the-mouth-is-so-insensitive-to-heat/383621/29 "2006-12-12T20:11:26Z")
[QUOTE=Bippy the Beardless] Even after the coffee has cooled down anough to gulp, it still hurts to put your finger in the coffee. [/QUOTE] When you drink hot coffee, you sip in maybe a tablespoon at a time. That small amount of coffee, while hot, doesn’t carry a lot of _heat_ because there’s just not enough mass to store a lot of energy. Your mouth has a large amount of mass and surface area, so the coffee cools down quickly and your mouth warms up slowly, never getting to a burning temperature. When you stick your finger in a cup of hot coffee, there is a lot of coffee mass, and little finger mass/surface area, so the coffee cools down slowly and your skin goes up in temperature quickly, right to the burning point. For an ill-advised test, suck down your cup of scalding hot coffee in a single mouthful, and hold it for a couple of seconds. Burn city. [Previous page](https://boards.straightdope.com/t/how-come-the-mouth-is-so-insensitive-to-heat/383621.md?page=1)