If you’re experiencing an itch, it might be your body’s way of alerting you to the presence of a foreign substance on your skin.
Factors such as dry skin flakes, dirt, insect bites, or even a stray hair can trigger an itch response, often prompting us to scratch in an attempt to remove the irritant. This reaction is effective in many situations, though not all.
A recent study conducted on mice suggests that this protective itching impulse might have its own specific sensory organ: vellus-like hairs.
In mice, these hairs are most abundant behind the ears and on the hind paws, areas where their skin is particularly exposed.
In contrast, humans are nearly entirely covered in vellus hairs, commonly known as ‘peach fuzz’, which are also associated with exposed skin areas.
Vellus hairs are crucial for regulating body temperature: they stand up when we’re cold and help to wick sweat away when we’re hot.
These hairs also appear to be involved in detecting certain types of touch, particularly those that trigger our urge to itch.
While there has been considerable research on itchiness caused by direct skin contact with irritants, researchers led by biologists at the University of Michigan identified a gap in studies exploring itchiness induced by hair movement.
“For instance, the gentle vibration of vellus hair on the chin, unlike on the forehead, face, or arms, causes intense itching in healthy human subjects,” the researchers mention in their paper published in Neuron.
“These findings suggest the presence of specialized hair structures and afferents dedicated to this form of mechanical itch.”
To further understand this, the researchers studied mice.
It’s important to note that while findings in mice don’t always translate directly to humans, our shared evolutionary history often provides useful insights.
“In humans, tactile perception is governed by two distinct types of hair: terminal and vellus hairs. In contrast, rodents have been studied for their pelage hairs, including guard, awl/auchene, and zig-zag types, which are essential for mechanosensation and thermoregulation,” the authors explain.
“Beyond these well-studied hair types in rodents, certain body regions feature atypical hair variants with unique functions.”
This leads us to the vellus-like hairs.
Through a series of experiments, the researchers found that each of these hairs is linked to specific fast-conducting sensory neurons that convey the sensation of an itch from a mere touch of the hair.
In mice experiencing chronic skin inflammation in areas with vellus-like hairs, these neurons were highly active, and the mice demonstrated signs of itchiness.
However, when the researchers disabled the genes responsible for these sensory neurons, the mice did not perceive the inflammation as itchy.
“These specialized hairs and their associated nerve terminals are crucial for regulating trichoknesis [itching triggered by hair contact] in chronic itch, underscoring their importance in abnormal sensory processing,” the researchers report.
Studying what causes mice to itch might seem unusual, but given the genetic similarities between mice and humans, these animals are frequently used in biomedical research to assess potential treatments for human conditions before clinical trials begin.
Understanding how this type of itching functions in mice—and its similarity to the human itch response from vellus hairs—suggests that mice could serve as suitable test subjects for developing treatments for human itching problems, such as insect bites, eczema, and poison ivy reactions.
Related: Scientists Uncover The Nerve Pathway That Makes Stress Worsen Eczema
“We need a new pathway to target if we want to treat chronic itch,” molecular biologist Bo Duan says.
“And our research suggests that this population of neurons could be a target in the future.”
The research was published in Neuron.
This article was fact-checked by Michael Irving and edited by Rebecca Dyer. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
