The National Institute of Dental and Craniofacial Research says the answer is a mixture of commonly held beliefs along with some interesting new research.
While it’s true that irritants on the skin, such as a rash or a insect landing on us, can trigger an itch through nerve cells, the process of how we are made aware of the sensation, clinically known as “pruritus,” takes part in different parts of the body.
Testing on mice, the scientists found that a molecule released in the dorsal horn of the spine begins the biological process. The molecule, neuropeptide natriuretic polypeptide b (Nppb), then travels to the brain, creating the feeling of the itch.
In their study, the scientists were able to isolate mice without Nppb. “When we exposed the Nppb-deficient mice to several itch-inducing substances, it was amazing to watch,” said Santosh Mishra, lead author on the study. “Nothing happened. The mice wouldn’t scratch.”
“The receptors were exactly in the right place in the dorsal horn,” added study co-author Mark Hoon. “We went further and removed the Npra neurons from the spinal cord. We wanted to see if their removal would short-circuit the itch, and it did.”
Through their research, the scientists learned some other fascinating facts about Nppb as well.
“It’s released by the heart,” Hoon told Time, “to control blood sodium and blood pressure. It’s a cornerstone of biology that a lot of these neurotransmitters are used in different parts of the body for different purposes.”
So, does that mean it’s time to take a celebratory dive into poison ivy? Do humans no longer have to worry about annoying itches?
Not exactly. Hoon says doctors would currently be faced with two undesirable options: Affecting blood pressure control or injecting Nppb directly into the spinal cord, which, he dryly notes, “is not a trivial thing to do.”
In the meantime, the study’s authors are hoping to solve the other end of the equation, finding out why itching stops.
“Now the challenge is to find similar biocircuitry in people, evaluate what’s there, and identify unique molecules that can be targeted to turn off chronic itch without causing unwanted side effects,” Hoon said in a release accompanying the study. “So, this is a start, not a finish.”