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Home experiment time! Go run some hot water, either in a sink or tub, and stick your hand under it.
Some of you might be mad at me—the water was hot and you have no idea why I asked you to scald yourself. (We’ll work through this.) Some of you, though, are going to be a little confused. You know the water was hot, but when you put your hand under it, it felt ice cold.
All together now, in your best Jerry Seinfeld voice: “What’s the deal with that?”
Feeling Spots
Our hands have a mess of sensory receptors that all receive different sensations. These receptors send signals to the brain to help us make sense of what we’re touching. We’ve got some receptors that receive sensations of cold (cold spots) and others that receive warmth (warm spots).
Neither of these temperature receptors pull double-duty. If you touch a cold spot with something hot, it’s still going to do what it’s supposed to do: send a cold signal. If you touch a warm spot with something cold, it’s still going to tell the brain that you’re touching something warm.
Mixed Signals
Neurologists call instances when these spots send the “wrong” signal in response to a stimulus paradoxical cold and paradoxical warmth. If you want to try another experiment (and you still trust me after the hot water thing), grab a pen and lightly poke the point around between your knuckles. In some spots it will feel cold, in some it will feel warm.
Of course, when you run your hand under hot water, the water touches both warm and cold spots. In cases like this, where the stimulus is strong enough, the receptors get confused and sometimes the wrong signal gets sent to the brain, even though both temperature receptors are being stimulated. Sometimes it only takes a second for things to correct themselves; sometimes it takes a few minutes.
How did the hot water experiment turn out for you?
If you’ve got a burning question that you’d like to see answered here, shoot me an email at flossymatt (at) gmail.com. Twitter users can also make nice with me and ask me questions there. Be sure to give me your name and location (and a link, if you want) so I can give you a little shout out.
Comments (37)
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Interesting! You have some points there!
posted by Rosabel on 8-27-2008 at 6:06 am
I remember an experiment in high school where you have a hose of warm water and a hose of cold water corkscrewing around each other. When you held them (together) it felt hot but apart they were warm or cold. That was fun.
posted by HunterJay on 8-27-2008 at 6:24 am
I remember when I was kid, probably around 10 yrs old or so, asking myself this very question. Now I know.
Thanks mental_floss!!!
posted by Justin L on 8-27-2008 at 8:47 am
OK, I have now officially poked holes practically through my skin and nothing. What and I doing wrong?
posted by GTT on 8-27-2008 at 9:38 am
People are staring at me, wondering why I’m poking myself at work…
This is pretty cool!
posted by Anthony on 8-27-2008 at 11:00 am
Ouch.
posted by mexichica on 8-27-2008 at 12:07 pm
Why doesn’t hot water feel hot when on your hand/arm/leg when you have poison ivy?
When you have poison ivy, putting it under HOT water, the water doesn’t feel hot at all, and it takes the “itchiness” away!
posted by Chris on 8-27-2008 at 8:58 pm
Your feet are much better at sensing temperature than your hands
posted by PartiallyDeflected on 8-27-2008 at 10:58 pm
I would conduct this experiment almost every night when I test the temperature of my shower water. I’ve always wondered about that, and now I know! Thanks!
posted by heather on 8-28-2008 at 1:22 am
What about when you have an itch in one spot of your body, but when scratching that itch, you feel it somewhere else?? Is that the same thing???
posted by colleen on 11-17-2008 at 12:45 pm
Hey colleen – I have wondered about that too – but even weirder, I think, is when I scratch my husband’s back and then I start getting itchy – check the website for an interesting article that may have something to do with it.
posted by Shmaem on 11-17-2008 at 1:10 pm
Yeah, that thing where you have an itch and when u itch it it pops up somewhere else, i get that too, it drives me crazy sometimes!
posted by mememememe on 11-17-2008 at 3:54 pm
omgoodness i hear what ya’ll are talkin about!! i hate itchy spots and then its like, “that’s not the right spot!!” then u itch somewhere else. its annoying. :D
posted by frog love on 11-27-2008 at 9:50 pm
Chris, I wouldn’t put hot water on poison ivy, it will cause it to spread.
posted by Jason on 12-2-2008 at 1:21 pm
Familiar Kitchen Joke. Take a sheet tray out of a refrigerator and touch it to someone. Most likely they’ll jump because they thought they were just burned.
Pretty Funny!
posted by Ryan on 12-8-2008 at 12:05 am
Maybe someone mentioned this, but heat transfer might be involved, as well. When you’re taking a shower, turn the water cold and run it over your head; the water is cold when it hits you, but when it runs down, it’s warm…the heat from your body is tranferring itself to the cold water. Same as when your warm hand touches cold metal and soon the two become the same.
posted by Cory on 12-12-2008 at 1:06 am
im doing the experiment in which you touch two different hoses, one warm one cold, and you feel that they are hot.
does anyone know why this happens?
or the name of this event?
email me at lantyem@aol.com
posted by luis on 1-2-2009 at 5:17 pm
I was just wondering what caused this. I’ve experienced it when dropping food in a pot of heated water (not yet boiling). It makes me do a doubletake as to whether the water is actually heated up or not.
posted by Alex on 2-12-2009 at 2:10 pm
This is pretty cool!!
posted by dude on 2-13-2009 at 1:28 am
I don’t think I’ve ever noticed this! But it really is interesting!
posted by The Road Virus on 3-7-2009 at 7:42 pm
This does not answer my question in the least because it doesn’t thoroughly explain WHY this happens. You may notice the effects of this even more so if you life in a region that get cold in the winter. Ever come in the house and run your cold outdoor hands under hot water (which you actually aren’t supposed to do)? The same thing (hot feels cold) lasts longer before you finally feel that it is hot but for some reason you can still tolerate it.
posted by bob on 3-7-2009 at 8:10 pm
I once was feeling the water in my baby’s tub and the coolest thing happened…I couldn’t feel that my hand was wet. It didn’t feel like ANYTHING! I had to do a double take to make sure my hand was in fact in the water, but I assumed it was probably at room temp or something. All I know is it didn’t feel wet, cold, or warm.
posted by eman on 3-7-2009 at 9:54 pm
eman,
That happened because the water was at the exact same temperature as your body.
bob,
I’ve done this too…weird huh?
posted by mon on 3-7-2009 at 10:31 pm
This happens a lot to me when I’m in the tub, when you put your feet under the running faucet water. Sometimes, when the water is really hot, it can feel honestly rather cold.
Always wondered about this. Thanks!
posted by Jennifer on 3-7-2009 at 10:32 pm
I did something like this as a science lab in high school, though we did a little more with it, and I found that sharp pains (like from a sewing needle that doesn’t break the skin)almost always feels hot, while blunt pressure (like a pencil eraser) feels cold if any specific temperature sensation is registered.
Does anyone else have this happen?
My theory is that the brain is wired to feel sharp/hot pain as something that could damage the body faster, as opposed to something blunt/cold so a more urgent sensation is created so you’ll aleviate the offending stimuli. Can anyone confirm or set me straight on what’s actually going on?
posted by Rini on 3-7-2009 at 11:17 pm
That usually only happens to me when my hands have been exposed to any temperature less than 40 degrees F. But the water feels cold and icy even though it’s not even that warm.
posted by ShiroKitsune on 3-7-2009 at 11:48 pm
the worst part of the whole hot/cold water receptors is when you put your hand in ice water for over a minute and then put it under cold running water and your hand feels like you just stuck it on a stove.
posted by Mike on 3-8-2009 at 1:05 am
On poison ivy/oak (same chemical). The hot water spreading deal comes from the oil in the leaves. If you wash it off with hot water, the oil spreads and therefore the inflammation will affect more skin. If you already have the inflammation and the oil is gone (you took a shower at some point and used soap) then the hot water has no spreading effect. Likewise washing immediately with a strong soap might be ok in hot water…hmmm…
posted by Nate on 3-8-2009 at 1:10 am
Psychologically speaking, I think you are right Rini. If I am remembering correctly from my psychiatry studies (no I’m not a psychiatrist, I’m studying to be one) then I think that yes we are hardwired to respond more quickly tp pain and heat because both have a good chance of harming us. So, from an Evolutionary Psychiatry standpoint, I do think you are correct.
As for the putting your hand in freezing cold water then just running cold water over it out of the faucet, I think the same stimulus applies, but in a different way. We are wired to notice certain things, but when it comes down to it I think physically the lowering of the temperature of the hands causes them to be more receptive towards warm objects. Just like in physics, the cold doesn’t transfer, it uses the energy of the heated objects to warm itself back up to a functional level. So, if we pretend that we are just physical beings, then when we have a cold hand, it more readily absorbs the warmer temperature of the “cold” water, and the speed at which it does this causes an information overload to your brain which says, “Hey! GTFO man!”
So, I think all of the above theories are correct, I just felt the need to somewhat explain them through physics and Psychiatry…sorry if I bored anyone.
~Motoko~
posted by Motoko on 3-8-2009 at 1:46 am
I suppose I’m normal yet unusual at the same time.. When I put my hand under hot water, it’s hot.. Cold is cold.. Maybe Hell will freeze over now?
posted by Tom on 3-8-2009 at 3:06 am
I just tried it, and the hot water felt hot, and cold felt cold. Didn’t work! Perhaps it doesn’t work on all.
posted by Elvisc on 3-8-2009 at 3:07 am
Going on a chicken, what is GTFO?
Back to the subject, I’ve done that before. It sucks hard.
posted by Azaurmyth on 3-17-2009 at 2:11 am
bob: It’s because the nerves/skin in your hands are themselves cold, and the hot water takes a bit to warm them up and make them active.
posted by trlkly on 5-4-2009 at 4:42 pm
Actually in my college anatomy class we learned that you sometimes feel hot water as cold because you have cold receptors, hot receptors, and extreme receptors that sense both extreme cold and extreme hot temperatures which is how they messages get crossed.
posted by Melissa on 6-4-2009 at 3:41 pm
GTFO- Get the F$#% Off!
posted by Tamsyn on 6-14-2009 at 4:46 pm
Hot water is good for other itchiness related instances though, such as mosquito bites. hot water tends to relieve the itchy sensation that the mosquito saliva in your skin is doing to you. cold water is good for burns. and finally, cold gradually progressing to warm is good for areas of the body that have been exposed to cold temperatures and is starting to turn red/blue/abnormally dark (the last one you might want to phone up a doctor).
posted by Steven on 7-23-2009 at 1:18 pm
This is pretty sick i tried the knuckle thing and it worked and so did the sharp and blunt pressure thing. I was looking for a science question involving high and low kinetic energy and his showed up.
posted by Gavin L. on 10-13-2009 at 11:09 pm