Why we itch, and why it’s so hard to stop

The bite.
The bite.
Image: CDC/ James Gathany
We may earn a commission from links on this page.

It’s as much a part of enjoying the warm summer months as camping, swimming, or sipping a glass of wine on the patio: The horrible high-pitched whine and the bite of the mosquito. And after the bite comes the worst part: the itch.

After millennia of dealing with the scourge of mosquitoes, you might think we technologically-advanced humans would have come up with a way to combat the itch (which is known medically as pruritus) that comes from bug bites and other sources.  

We have treatments for many other common ailments: If you have a headache, sore joints, or a minor toothache, aspirin, ibuprofen or naproxen (Aleve) will likely take care of the problem for a few hours. Not so the itch. The reality is that there is no effective and long-term over-the-counter way to get rid of that infuriating itchy sensation. Itches are annoying for everyone, but they can be more seriously debilitating: Some suffer from chronic itch, and at the moment, there is no proven cure.

On a recent reporting trip to South Texas, I was set upon by scores of mosquitoes every time I got out of my car. By the end of my trip, my arms, neck and back were dotted with a galaxy of red welts that itched like crazy. When I asked my doctor to recommend the best itch remedy, he pointed me to topical solutions such as calamine lotion and Hydrocortisone. I tried both, and neither worked well after 10 minutes or so. The itch kept coming back. I called my doctor again, asking what more there was to do. Not much, he said.

“In the end, you’re probably just better off using ice,” he said. “It’s not perfect, but it should suffice.”

It didn’t. 

Instead, I became deeply curious about why this seemingly simple human discomfort was so difficult to remedy. It turns out the answer was more complicated than I thought. And there’s a shred of hope: We are in the midst of a revolution in itch research.

Diana Bautista, an associate professor of cell and developmental biology at the University of California, Berkeley, says that in the last decade, our understanding of acute itch has skyrocketed.  

We know why skin itches after a mosquito bite: The body reacts to a compound that the insect delivers through its mouthparts to prevent the blood it’s sucking from clotting. What’s puzzling to scientists is that, unlike touch and other sensations, itch does not seem to have a particular location in the brain where it is localized. While looking at the brain of itch sufferers in an MRI machine, numerous areas light up, and once the patient scratches the affected area, whole other parts of the brain fire up, too—the areas linked to reward, pleasure, craving, and addiction.    

“It’s very complex and means that there’s no one target in the brain which would solve itch,” Gil Yosipovitch, a dermatologist and neurobiologist known as “the Godfather of Itch,” told Quartz.  Yosipovitch is the director of the Miami Itch Center at the University of Miami.

Your body and brain have numerous types of receptors for different kinds of feeling and how to process them, and can differentiate between an astonishing number of tactile inputs. It can sense warmth and cold. It immediately knows when we you’re touching a piece of wood, a fellow human, or the soft fur of a puppy.

For decades, scientists thought that pain and itch where part the same receptor, although it was uncertain which one.  But they were wrong. “Just a few years ago, there were huge misunderstandings about itch,” Brian Kim, who runs the Center for the Study of Itch at Washington University School of Medicine in St. Louis, told Quartz. “It was not viewed as a distinct biological pathway. So people thought that the way to solve itch was to study pain better.”

In 2007, scientists now working at the Center for the Study of Itch identified the first itch-specific receptor. Called the Gastrin-releasing peptide receptor (GRPR), the discovery has led to major advances in our understanding of the fundamental mechanisms of itch. Several other itch-specific receptors have since been discovered.

“A receptor is the equivalent of a keyhole or a lock,” says Kim. Different sensations require different keys to unlock the door to a feeling, and “itch has its own lock.” Knowing the type of lock you’re dealing with makes it a lot easier to find a key to open it.

Targeting receptors with drugs has become a particularly effective way to treat numerous diseases, including hypertension, allergies and obesity. Understanding the mechanics of these receptors has dramatically improved scientists’ ability to pinpoint where itch is first perceived and how it can be treated. 

One simple way to think about how pain and itch differ is to consider our reaction to both stimuli: pain creates a withdrawal reflex—for example, when you involuntarily snatch your hand away from a flame or hot pan handle. Itch, meanwhile, leads to a scratch reflex, the immediate need to stop the feeling by dragging your fingernails across the irritated area. Each is a different response, caused by different biological processes with different evolutionary origins.

Scientists don’t really know the evolutionary purpose of itch, but some speculate that it serves as a type of defense mechanism against parasites and insects that prompt us to scratch and thereby expel the organism from your skin.

“We used to be outside constantly, and we really needed some way to prevent serious infection, to quickly detect something crawling on your skin and to stop the infection that occurred if something burrowed even deeper and laid eggs,” says Ms. Bautista.

Of course, there are numerous reasons we itch that go beyond insect bites or a case of poison ivy. Dry skin, scab healing, and skin conditions like psoriasis, eczema, and athlete’s foot all lead to some form of itching. Itching also affects the elderly disproportionately. Some people have reported cases of itch that seem to stem from deep-seated neurological disorders having nothing to do with any external stimulus or irritant.  A terrifying New Yorker story from 2008 documented the case of a woman whose mysterious itch was so bad, she scratched through her scalp down to her skull and into her brain. A recent study showed that some forms of chronic itch may be the result of a defect in the immune system of some people.

“The problem with itch is that so many things lead to itch by their own path, which is not really the case with pain,” says Kim. The result is that, “the treatments for pain have been light years ahead of itch.”

But that may be changing. While itch is still very much a black box, Mr. Kim says that his lab has recently made great strides in better understanding where itch comes from and how to treat it. In his lab, patients who suffer from chronic itch have experienced “dramatic improvements” in clinical trials of two compounds: tofacitinib and dupilumab, both of which began as ways to treat inflammation. However, both drugs have proven side effects and are expensive.

But ongoing research to develop cheaper and derivative forms of itch treatment are currently underway. The initial target of these studies is chronic itch, which some studies say affects as much as 15 percent of the population.

None of this will offer immediate relief to me on my next reporting trip, but with research rapidly accelerating, help might soon be on the way.