Why Won't That Itch Go Away?

From mosquito bites to mysterious prickles, there’s just something oh so satisfying about scratching an itch. But how do the uncomfortable, skin tingling sensations make themselves known?

According to scientists, the prickly discomfort of a bites, allergic reactions and other skin irritations activate itch-sensitive nerve cells in the spinal cord. The neurons then spark conversation with a structure near the base of the brain called the parabrachial nucleus (PBN). This region plays a key role in receiving information about other sensations, including pain and taste.

From the spine to the brain, and beyond…

It’s here that the mystery begins. While scientists have been able to identify the role of spinal cord nerve cells and the parabrachial nucleus, they’re unsure where itch signals ultimately end up.

“The parabrachial nucleus is just the first relay centre for [itch signals] going into the brain,” explains neuroscientist and study co-author Yan-Gang Sun.

Scientists itching to solve the mystery

While previous studies have explored the way an itch registers on the skin, how the signals actually travel to the brain has posed a much harder question. For Zhou-Feng Chen, director of the Centre for the Study of Itch at Washington University School of Medicine, the research is a “major step” toward solving the mystery.

The team are currently conducting a series of experiments on mice that are injected with a drug that induces allergic itching. As expected, activity spiked in the neurons that connect the spinal cord to the PBN. In another experiment neurons travelling to the PBN were made light-sensitive. Light was then used to stop the neurons from sending messages, which actively blocked nerve cells and caused the mice to scratch less.

Allergic vs anecdotal

While it’s too soon to confirm whether human itch signals follow the same route, the team is optimistic. That said, they were quick to admit that allergic itches are markedly different from those caused by physical variables like touch. As such, the two sensations could be handled differently by the brain which would open a whole new realm of research. Plus, unlike humans mice aren’t able to describe their itchy sensations. This means that scientists are forced to rely on clues like scratching, which is simply a physical reaction to an itch, not a candid measurement of the sensation itself.

In any lab, accuracy always takes centre stage. For a closer look at how scientists maintain precision don’t miss ‘Different Measuring Techniques Provide Different Results – But What is the Truth?’