Itching Is As Much In Your Brain As On Your Skin

By Debra Kelly on Monday, April 6, 2015
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“I can’t help it, Charlie. I itch when I’m nervous!” —Itchy Itchiford, “All Dogs Go to Heaven” (1989)

In A Nutshell

An itch is defined as a sensation that makes you want to scratch it, and it’s thought that the itching sensation and the pain sensations were somehow connected. Now, researchers have been able to isolate the chemical in our bodies that’s responsible for transmitting the sensation of an itch to our brains and have successfully engineered mice that can continue to respond to other sensations while no longer being itchy. The discovery can have some incredible implications for those suffering from chronic itch, like the woman who scratched through her own skull and into her brain in an attempt to relieve the relentless itch.

The Whole Bushel

Itching is a weird thing. It can be absolutely maddening, happen for no apparent reason whatsoever, and scratching it can provide a tremendous amount of relief—even if that scratching relief means you’re leaving red marks on your skin. It’s one of those things that we’ve all experienced (and you’ll probably be experiencing it quite soon, after just reading about it) but that science knows only a little about.

Our first definition of the itch came in 1660, from a German doctor named Samuel Hafenreffer, and he’s the one who defined it as a sensation in the skin that made you want to scratch it. Pretty straightforward, but just how much of the itch is skin-related and how much is brain-related has long been up for debate.

And, it looks more and more like it’s just about all in your head.

There are things that will make your skin physically itch, for sure. There are irritants and bug bites, allergies, and rashes. But science has made some pretty incredible discoveries that suggest that most of that itchy feeling is really all in your head.

There’s a single chemical that researchers are pretty sure is responsible for our ability to feel itchy, and it’s called Nppb, or natriuretic polypeptide b. Molecular geneticists from the National Institute of Health have isolated the compound and have found that removing it also removes the feeling of being itchy.

Working with mice, the scientists first isolated the different chemical transmitters that were responsible for passing sensory information through the body, including reactions to heat, cold, and pain. They then started genetically engineering mice to remove some of those chemicals, and the mice with no Nppb stopped reacting to the normal itchy sensations that were created when they were exposed to different types of histamines.

Nppb is paired with specific neurons, called Npra. In mice where these were removed, the chain of itching was also stopped, showing that there’s a very specific way the sensation of itching is transmitted. No other reactions or sensations were impacted either.

Other research has proven that our itch receptors are incredibly sensitive and that an itch nerve or fiber will react to stimuli as far away as 7.6 centimeters (3 in). Factor in the findings that itching is defined by a desire to scratch, and it all seems to support the idea that itching was developed very, very early on as a way for the body to defend itself against potentially toxic substances.

There’s nothing that gets your attention quite like a relentless itch, after all.

So how much of the itch is in your skin and how much of it is in your brain?

The removal of the Nppb and Npra neurons and the complete lack of itching suggests that quite a lot of it is all in our heads, but our heads aren’t always rational—at least at a glance. Itching has long been associated with pain—it’s the pain of scratching that overrides and gets rid of the itch, after all—but the recent research shows that they’re two entirely different, independent things. And that might have some serious impact on those suffering from chronic itch, which can be caused by a huge number of conditions.

And, as if that’s not troublesome enough, we’ll end on a pretty horrific story of chronic itching. A patient called only “M” developed a chronic, troublesome scalp itch that had no apparent cause. Her life had fallen apart, and she was on her way to putting it back together when her unstoppable itch started. Nights were the worst, but the worst night of them all was most likely the one where she woke up with a green liquid running down her face. When she went to the doctor, she was rushed to surgery immediately. The itch had gotten so bad that in the night she had torn through her scalp and scratched through her skull (which had been softened by a bone infection) and into her brain.

Show Me The Proof

Smithsonian: Discovered: The Molecule Responsible for Itchiness
LiveScience: Scratching Away at the Mystery of Itch
New Yorker: The Itch