May 4 (UPI) -- A severe reaction to light touching -- often among old people -- occurs because of fewer receptors in the skin, according to a new study with mice.
Researchers at Washington University School of Medicine in St. Louis studied severe itching from light tough, even when the skin is under clothing. Their findings, which researchers hope will lead to a treatment for the condition, were published Friday in the journal Science.
"Itching caused by touch becomes more common as we age and is especially problematic for people with dry skin or who already suffer from chronic itching," senior investigator Dr. Hongzhen Hu, an associate professor of anesthesiology at Washington University, said in a press release. "It can be more than a nuisance, and there are no drugs available to treat this type of itching, so we wanted to identify the underlying causes in hopes of finding better ways to treat it."
Hu conducts research as part of the university's Center for the Study of Itch.
They found animals with dry skin had fewer receptors, and that the number of touch receptors in the skin, called Merkel cells, declined as mice aged.
"As the number of Merkel cells went down, problems with touch-related itch went up," Hu said. "What exactly Merkel cells do has not been clear, but our findings suggest they help control the itch response. When you lose these cells, their ability to inhibit itch also is lost."
When researchers activated Merkel cells in genetically engineered mice using a chemical compound, they found the mice were more likely to scratch when touched with a hairlike device.
"This gives us hope that if we can control the activity of the Merkel cells themselves, we may be able to control this type of itching," first author Dr. Jing Feng, a postdoctoral fellow at Washington's School of Medicine, said.
Researchers found a protein called Piezo2, which is made on the membranes of Merkel cells, also plays a role in controlling the cells and reducing itchiness.
The researchers are now studying skin samples from humans with touch-related itch problems to see if the findings will translate to methods for human treatment.
"As people age, their skin changes, and for some people this can lead to severe, intractable itching," said Dr. Brian S. Kim, a co-director of the Center for the Study of Itch. "For example, many of my patients with severe, chronic itch associated with aging cannot tolerate certain types of clothing. That observation fits with Dr. Hu's findings that these receptors in the skin suppress itch, but with aging, the cells disappear, and normal touch sensations can be perceived by some patients as pathologic itch."