Can Science Explain How Hot Water Stops Itch?

Spending time outside in the summer is usually delightful. Even with the pandemic, people are still able to enjoy gardening, hiking and other outdoor activities, at appropriate distances from others. There’s one big drawback. Encounters with chiggers, mosquitoes and poison ivy can result in terrible itching. What can you do to calm it? Do we know why a blast of hot water stops itch instantly?

Hot Water Stops Itch Like Magic:

Many people resort to cortisone cream. While it can help, we have always found that a simple home remedy can be equally effective.

Hot water is as close as the kitchen sink. It is surprisingly effective against almost any itch. (The exception is hives; hot water may make it worse.)

We first learned about this amazing remedy from a 1961 textbook, Dermatology: Diagnosis and Treatment. The expert recommended very short exposure to hot water (120 to 130 degrees F). It only takes a second or two to overwhelm the itch sensation from the upper layer of the skin. You can run water over the itchy area straight out of the tap or use a washcloth to cover a place that is hard to reach. The relief may last for a couple of hours.

Why Hot Water Stops Itch:

How does hot water work? Nobody knew it back in the 1960s, but nerves have specialized receptor channels to detect heat and cold (Temperature, April 29, 2019). These transient receptor potential (TRP) channels play a role in many functions within the body. They also respond to a number of chemicals, such as capsaicin, the hot stuff in hot peppers (Nature, Oct. 23, 1997). We suspect that  TRPV1 is key in this case (International Journal of Molecular Sciences, June 23, 2020). More recent research confirmed that TRP channels moderate itch (Neuroscience Bulletin, Feb. 2018).

Even though the dermatologists of yore didn’t know the names of these receptors, they suspected that hot water could short-circuit the neuronal itch reflex. Heat overloads the nerve network so effectively that the urge to scratch is abolished for hours. Relief usually comes within seconds.

Here is what some of our readers have to say:

“Oh my gosh, hot water on a severe itch brings marvelous relief for a few seconds and then the itch stays away for hours. It’s an addicting feeling. I have a rash right now, and I am actually looking forward to when it starts to itch again so I can use the hot water trick. It’s kind of embarrassing how good it feels, almost like you should be somewhere very private when you do it.”

Another reader harkens back several decades:

“I learned about the hot water method from my mom, a practical nurse, back in the 1970s. She said the hospital where she worked was experimenting with this method to treat patients with severe itching. I have used the hot water method successfully for flea, mosquito and poison ivy itch.”

Finally, a third reader has a complex regimen:

“When I get a mosquito bite, the intense itching lasts for several days. Prescription cortisone creams or oral antihistamines don’t seem to help.

“I use a combination strategy. Hot water is my first choice because it is fast and effective. The water has to be almost hot enough to hurt, but not to the point that it could burn. The Bite Helper [a device that generates heat to apply to a spot on the skin] is useful, but I go through lots of batteries fast!

“Finally, if these first two options aren’t convenient, I use a one-two punch with topical creams. I first apply Biofreeze gel, which has 4% menthol. After a minute or two, as I feel it start to cool and tingle at the bite site, I then apply Benadryl camphor gel with 0.45% camphor. That provides instant relief from even the most intense itch, due to the cooling sensation of the two gels.”

Menthol activates the TRPM8 channel (Journal of Investigative Dermatology, June 2018) and calms itch. (By the way, readers report that Vicks VapoRub, with its menthol and camphor, calms the itch of mosquito bites.)

Although we don’t know quite how camphor works against itch, many people seem to find it is helpful. Consequently, we’re not surprised this formula would work. Sometimes it takes decades to find out why an old-fashioned remedy actually works. Now you know how hot water stops itch!