Outliers: Need to scratch that itch? Researchers may know why

It's a familiar sensation, particularly among lovers of wool sweaters or frequent victims of insect bites, but itchiness and its causes have long been a source of contentious debate among scientists. Researchers at Johns Hopkins University School of Medicine now think they may have come up with an answer to the burning question, “Why do we itch?”

The scientists say they have identified specific nerve cells in mice that are responsible for sending itch signals to the nervous system. Their findings, published in the journal Nature Neuroscience, could settle decades of bickering about how the human body processes feelings of pain versus feelings of itch.

The infighting has been fueled by uncertainty about whether certain nerve cells, equipped to respond to both itchy and painful stimuli, were sending both signals to the brain. Based on these latest findings, researchers concluded that nerve cells with an itch receptor known as MrgA3 send itch messages to the brain whether they're exposed to painful or itchy stimuli.

In one of their experiments, researchers bred mice so that their MrgA3 cells were the only cells capable of responding to a pain-producing peppery substance. After injecting the substance into the cheeks of the mice, the scientists observed their furry subjects frantically scratching their little mouse cheeks instead of massaging their mouths in pain, as was expected. (Outliers apologizes to any mice-loving readers.)

That reaction suggested to the research team that MrgA3 cells were sending itch messages regardless of the stimulus.

“Now that we have disentangled these itchy sensations from the painful ones, we should be able to design drugs that target itch-specific nerve cells to combat chronic itchiness,” said Xinzhong Dong, an associate professor in neuroscience at Johns Hopkins and the study's lead author.

But there could still be some rough patches ahead. The scientists acknowledged in the study that MrgA3 cells may not be the only nerve cells in the body to respond to itchy stimuli, suggesting they might just be starting to scratch the surface of the problem.