NEA-Funded Research on Itch Shows Atopic Dermatitis Patients React Differently to Heat and Scratching

At the urging of many patients, NEA is directing a substantial portion of its research funds toward studies on itch. Recent NEA funded research supports the idea that itch modulation is abnormal in patients with atopic dermatitis; it could be associated with nerve fibers that are overly sensitive to itch.

In the January issue of the British Journal of Dermatology, Dr. Gil Yosipovitch and colleagues from Wake Forest University Baptist Medical Center in Winston-Salem, North Carolina, reported on their study to examine the effects of repetitive heat and scratching on itch intensity in 16 patients with atopic dermatitis and 10 healthy subjects.

For decades, the application of painful stimuli has been suggested as a method to inhibit itch, and patients with chronic itch do often report that very hot showers relieve their itch. Until now, however, no studies had been performed to assess the effects of repetitive heat and scratching on itch.

To conduct the first such study, the Wake Forest researchers used a non-invasive method (iontophoresis) to propel small amounts of histamine, a protein that causes allergic reactions, under the skin of study subjects. They then scratched near the affected area (within 3 cm) with a small brush or applied a heated device (120 degrees Fahrenheit) for a short period.
The researchers found that neither heat nor scratching inhibited itch in people with atopic dermatitis, but they did so in healthy skin. In fact, both heat and scratching increased itch intensity in patients with skin lesions.

“Our results strongly suggest that scratching and heat have a different effect on patients with atopic dermatitis than on those with healthy skin,” said Yosipovitch. “This difference may be associated with both peripheral and central sensitization of nerve fibers in atopic dermatitis.”

Previous studies had shown that a single application of a painful stimulus— either electrical, chemical, or heat—is often perceived as itch when it is applied on or near skin lesions in people with atopic dermatitis. These studies led to the theory that neural sensitization is involved in this altered itch perception in atopic dermatitis. The study by Yosipovitch and colleagues was unable to explain why patients with atopic dermatitis often report that scratching and hot showers are the only way to reduce itch. Yosipovitch said his study did not use harsh methods of scratching and that the heat cycles were of short duration. He said it’s possible that patients engage in harsh scratching and prolonged hot showers, which may inhibit their itch.

“However, it’s clear that these methods damage the skin in the long run and could make the itch-scratch cycle worse,” he said.