Why stress makes itch fade; IISc maps the brain circuit

Researchers at the Indian Institute of Science (IISc) have identified a brain circuit that helps explain why itching reduces during moments of acute stress.

The findings, published in the journal Cell Reports, shed light on how an emotional state can influence physical sensations.

Itch and pain are both unpleasant responses to irritation, but they trigger different reactions. Pain usually causes a person to withdraw, while itch leads to scratching. Although scientists have studied how stress affects pain, its impact on itch has remained less clear.

A team of researchers from IISc focused on the lateral hypothalamic area, a region of the brain known to regulate stress and emotions. Using genetically engineered mouse models, they identified a group of neurons in this region that become active during short-term stress.

When researchers activated these stress-related neurons, scratching behaviour reduced in mice experiencing both short-term chemically induced itch and a psoriasis-like chronic itch. When the same neurons were silenced, stress no longer reduced scratching. This showed that the neurons play a key role in suppressing an itch during acute stress.

The study, led by Jagat Narayan Prajapati and Arnab Barik in collaboration with Aynal Haque and Giriraj Sahu, also uncovered differences between acute and chronic itch.

In mice with long-term inflammation resembling psoriasis, these stress-sensitive neurons became more excitable and behaved differently, preventing the usual suppression of itch. The findings suggest that chronic stress may worsen persistent itching by altering brain circuits.

A chronic itch affects millions worldwide, and most treatments focus on the skin or immune system.

“Most current treatments for chronic itch are peripheral — they treat the symptoms, not the cause. But the interaction between stress, anxiety, and sensations like itch happens in the brain,” Barik explains. “Understanding these circuits gives us a framework for eventually developing therapies that address the central mechanisms underlying stress-related itch.”