Next time you struggle to resist an itchy rash or insect bite, you could find relief in the mirror.

Perception of our own bodies can be easily manipulated using tricks such as the rubber hand illusion, which fools people into thinking a rubber hand is their own. Reflecting someone’s limb in a mirror has also been used to treat phantom limb pain.

Now Christoph Helmchen and his colleagues at the University of Lübeck in Germany have shown that a similar mirror illusion can fool people into feeling relief from an itch, even when they scratch the wrong place.

The team injected the right forearms of 26 male volunteers with itch-inducing chemical histamine. Because the injection creates a red spot, they painted a corresponding dot on the opposite arm so both looked identical.


One of the researchers then scratched each arm in turn. Unsurprisingly, scratching the itchy arm produced relief, while scratching the other one did not.

Sweet relief

Next, they placed a large vertical mirror in front of the itchy arm, blocking off the subject’s view of their right arm and reflecting back the non-itchy one in its place . They asked the volunteers to look only at the reflected limb in the mirror, whilst a member of the team again scratched each arm.

This time the participants felt relief when the unaffected, reflected arm was scratched.

Although the effect was relatively weak – the relief from mirror scratching is about a quarter of that from scratching the real itch – the study shows that visual signals to the brain can override messages from the body if there is a mismatch between them.

Francis McGlone at Liverpool John Moores University, UK, thinks the finding could lead to treatments for chronic itching – a debilitating but poorly understood condition in which patients will often scratch their skin until it bleeds. “This paper adds important insights into the complex mechanisms underlying itch – an often ignored sensory channel, but one that can have devastating consequences on quality of life for patients,” he says.

Journal reference: PloS One, DOI: 10.1371/journal.pone.0082756