The Mechanism Behind Chronic Itching: Why You Scratch

Do you feel itchy? Ever spend a sleepless night scratching? Now, scientists have revealed the mechanism behind chronic itching, which could help develop treatments in the future.

Chronic itching can occur in many medical conditions. It can happen in eczema and psoriasis or kidney failure and liver disease. Unlike the fleeting urge to scratch a mosquito bite, chronic itching is persistent and seems to incorporate more than just the nerve cells, or neurons, that normally transmit itch signals.

"In normal itching, there's a fixed pathway that transmits the itch signals," said Zhou-Feng Chen, one of the researchers, in a news release. "But with chronic itching, many neurons can be turned into itch neurons, including those that typically transmit pain signals. That helps explain why chronic itching can be so excruciating."

In order to examine chronic itching a bit more closely, the researchers turned to mice. More specifically, they created mice in which a protein called BRAF always is active and continually sends signals inside itch neurons. The BRAF gene and the protein it makes are involved in the body's pain response, but scientists weren't sure whether the gene also played a role in itching.

It turns out that the mice began scratching themselves spontaneously, which revealed that the mice felt itching rather than pain. In addition, further studies found that the BRAF protein could turn on many itch genes, and they showed similar changes of gene expression in mice with chronic itch induced by dry skin and in mice with allergic contact dermatitis.

The findings reveal a little more about chronic itching. Not only that, they suggest a potential treatment for scratching. Targeting proteins in the BRAF pathway may open new avenues for treating chronic itch, a condition in which few therapies are effective.

"Certain drugs are used to inhibit some of the same targets in patients with chronic pain, and those medications also may quiet down itch," said Chen in a news release. "These mice are helping us to understand the pathways that can be involved in transmitting itch signals and the many contributors to chronic itching. There are many pathways leading from BRAF, and all of these could be potential targest for anti-itch therapies."

The findings are published in the Journal of Clinical Investigation.