Hot water on mosquito bites gets rid of the itch. But how, exactly?

August 7, 2013 11:53 AM

Dear life scientists! Please explain to me why hot water/heat makes mosquito bites stop itching.

Googling gives me:

- It makes the skin release histamines all at once
- It confuses the nervous system
- It short-circuits the nerves on your skin
- It cancels out the mosquito saliva/proteins/venom's anti-coagulating effect

I'm not sure what to believe! My last Biology class was 15 years ago but feel free to go into technical detail.

Thanks!

posted by ipsative to Science & Nature (10 answers total)

Best answer: This Straightdope forum post includes this sketchy memory from the poster's neuroscience days:

pain, itching, and extreme temperature (both hot and cold) are all relayed along the same nerve pathway. This pathway has a feedback loop at the sensory end, which will "turn off" the nerve if the sensation becomes too intense. So, if you run water that is so hot it triggers the "pain-itch" pathway instead of the "heat" pathway, you may eventually overload the pain-itch pathway and shut it down.

Note, that's for general itching. And this page on Insects.About.com says that "when the blood vessels expand, nerves in the area become irritated by the swelling. You feel this irritation as an itchy sensation."

If this is all true, then it makes sense that heat or cold would cancel itching caused by mosquito bites.
posted by filthy light thief at 12:06 PM on August 7, 2013 [3 favorites]

There are probably several things happening in your skin when bitten that are all working together to provide such a plethora of explanations. I'll go with the protein explanation.

Heat can force proteins to twist into different configurations, and if the temp is high enough it can totally destroy proteins. Different proteins are susceptible at different temperatures. I was always under the impression that the "itchy" proteins in mosquito saliva got twisted into a "non-itchy" configuration at "warm" temps like a hot bath or shower, thus temporarily stopping the itch. Applying more extreme heat (like the back of a spoon that's just been used to stir hot tea or coffee) will destroy them completely and make the itch stop for good.

I did use the hot spoon trick just last weekend on a couple bites. As soon as I noticed the itch, I applied the heat (~5 seconds) and they never itched again. So even if my explanation of the reasoning is a bit off, the end result is still what you want :)
posted by trivia genius at 12:09 PM on August 7, 2013 [1 favorite]

There's this gadget that apparently "works on the principle that most insect venom is thermolabile (sensitive to heat)."
posted by Empidonax at 12:12 PM on August 7, 2013 [1 favorite]

Also works, in a delicious way - not just relief, but a hard-to-describe pleasure - for poison ivy, so less likely to be a counter to mosquito proteins.
posted by bullatony at 12:34 PM on August 7, 2013 [3 favorites]

According to this Dr. Weil article about hot water and poison oak, it overloads the nerves.
posted by Dansaman at 1:00 PM on August 7, 2013 [2 favorites]

Best answer: Cecil Adams on the subject of how itching works. What happens in the nervous system to cause itching in the first place is not yet well understood: "Reading through the journals about the neurology of itching, you get the sense of well-meaning folk poking around in an extremely tangled fuse box."
posted by Johnny Assay at 1:51 PM on August 7, 2013 [2 favorites]

Itch is very understudied phenomenon. Unfortunately, I don't think Straight Dope or even more authoritative sources (sorry, Uncle Cecil!) really have the answer you're seeking at this point.
posted by karbonokapi at 2:25 PM on August 7, 2013

it is the bomb for poison ivy. its like magnets: who knows how it works? probably magic.
posted by jpe at 4:13 PM on August 7, 2013 [1 favorite]

Best answer: My understanding based on a series of Robert Sapolsky lectures I listened to earlier in the year on stress and endocrinology/the nervous system tallies with filthy light thief's explanation. Namely (and grossly oversimplified), you have two different types of neurons for pain. Neurons for chronic pain (ouchies that don't go away, like itching), and neurons for acute pain (like cutting yourself or burning yourself). When acute pain neurons are activated, a "switch" is also activated that will switch them off after a short delay without further stimulus, so you get a short, sharp pain that goes away if there are no more activation signals.

Chronic pain neurons do not activate this "switch". However they are also switched off by it. So when you trigger the acute pain neuron, when it switches off, it will take the chronic pain neuron with it.

That's the theory at any rate. My terminology is likely incredibly wrong and bad, but you get the idea.
posted by smoke at 6:11 PM on August 7, 2013 [3 favorites]

Best answer: I know this is a year late, but the answer I learned when I was in medical school:

The symptoms of allergic reactions (redness, itching, swelling) are caused by the release of histamines. Histamines are stored in cells called mast cells that are circulating in the bloodstream. When there is an allergen present, mast cells are summoned to the area and "degranulate," or release their histamines, which are the cause of the local reaction you see in an insect bite. Typically the histamines, which have a short lifespan, are released at a slow and steady rate and the mast cell has time to make more histamines in the meantime so it doesn't run out for a few days. Very hot temperatures, however, will cause the mast cells to freak out and release all their histamines at once. Which is why you get the initially REALLY REALLY ITCHY OH MY GOSH sensation at first. But then, all the histamines are gone and the cell hasn't had time to make any more yet. So the itching actually goes away for a period of time until more histamines can be produced.

Disclaimer: I can't remember my source exactly. I know that I've either read this, heard it in a lecture, or heard the allergist I work with say it. I also can't say whether or not the other theories put forth to answer this question might also have some contribution to the process.

Hope this helped!
posted by alysonagain at 1:29 PM on July 3, 2014 [1 favorite]