How peach fuzz could hold clues to develop new treatments for chronic itch
Researchers discover specialized neurons and vellus-like hair in mice—hairs that are like vellus hairs, or peach fuzz, on humans—give rise to itchiness in response to touch
Working with mouse models, research led by the University of Michigan has revealed previously hidden biology of how touch-sensitive hairs create itching sensations. This fundamental discovery opens new avenues to better understand and potentially address human health conditions characterized by persistent itchiness.
"Itch is one of the major symptoms in most chronic skin inflammation patients," said Bo Duan, associate professor in the Department of Molecular, Cellular, and Developmental Biology. "What we've discovered is a pathway that we believe plays a very important role for both acute and chronic itch sensation."
The team discovered a previously unrecognized class of hairs in mice, known as vellus-like hairs, and a specialized population of touch-sensitive neurons that connect to them. As their name suggests, these hairs are similar to the fine, short, light-colored vellus hairs found on humans, though we more commonly refer to them as peach fuzz.
The work, supported in part by funding from the National Institutes of Health, was published in the journal Neuron.
For one set of experiments, the team worked with mice that had chronic skin inflammation, which is known as eczema in humans. Mice that expressed these neurons scratched normally, as one would expect. But, for mice that lacked those neurons or in which the neurons were inactive, the itching response was greatly reduced.
While there are a number of ways to help soothe chemical itch caused by things like mosquito bites and poison ivy, those treatments are ineffective against itch caused by skin inflammation, Duan said. This study suggests treatments that target the "mechanical itch" pathway could be more successful.
"We need a new pathway to target if we want to treat chronic itch," Duan said. "And our research suggests that this population of neurons could be a target in the future. We have ongoing projects looking at this."
Although the team can't run experiments to directly identify the same or related pathways in humans, the researchers are already building the case with other forms of evidence. For starters, humans do possess genes required to make these touch-sensitive neurons.
The team also discovered proteins in mice that help transmit the itch signal from hairs to the spinal cord via the specialized neurons. Human neurons grown in cultures respond to the same proteins, the team found.
"Our study indicates that humans may have this same kind of mechanism to transmit mechanical itch," Duan said. "It also reveals that the body has a dedicated system for this type of sensation."
A real head-scratcher
It's one of Duan's favorite science demonstrations, one that he gave while interviewing for his job and one that he still shows to students joining his lab.
First, you take a tissue and roll one of its corners into a long, fine point. Then take that point and, ever so gently, stroke at the hairs around your lips. Not the thicker, darker hairs, which are called terminal hairs, but the thin, light vellus hairs. If you graze one just right, that peach fuzz will make you itch.
"Humans and animals experience this kind of itch, but no one knew the molecular and cellular mechanisms behind it," Duan said. The new study identifies the sensory pathway that links specialized hairs to itch and, together with earlier research from Duan and his teammates, helps explain how these signals are transmitted through the nervous system.
It was more than a century ago that scientists first noted that the vellus-like hairs of mice, which are especially concentrated behind their ears, beneath their lips and at the base of their paws, were "special." Yet these hairs have remained largely understudied in sensory science, Duan said.
Because of that, there really weren't any standard procedures to test whether and how mice responded to mechanical itch. That meant Duan and his colleagues had to develop their own methods.
"A mouse can't say that it's itchy," Duan said. "But it will scratch."
For the new study, the team mechanically stimulated itch in mice using a small loop of thread and stroking the animal's vellus-like hairs. Once they identified the neurons that gave rise to the itching response, the researchers could then make those neurons sensitive to blue light. Shining light on a mouse's skin and observing it scratch in the same way it did with mechanical stimulation helped confirm the specific neurons' role in itch.
Peach fuzz and peach fuzz-like hairs grow in higher numbers near human and mice mouths and ears, Duan said. This suggests they may have evolved as a warning system for mammals to alert them when pests or parasites are trying to get in.
But human bodies are covered in vellus hair (with some notable exceptions like the palms of our hands) and you may wonder why we're not constantly scratching if we're coated with such sensitive touch receptors. Another one of Duan's earlier projects studying itch in mice could also explain that: Within the spinal cord, there are "gating" circuits at work that essentially block the mechanical itch signal unless it's activated in a particular way.
Journal
Neuron
Article Title
A Specialized Population of Hair Afferents Dedicated to Transmitting Mechanical Itch
Article Publication Date
4-Jun-2026
No comments:
Post a Comment