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A mosquito bite itches. Tickling under your foot itches. But you can also get itchy without a physical stimulus. Itching researcher Danielle Bartels of Leiden University: ‘Because you expect itching, for example, or when you talk about itching or see someone else scratching. That’s what we call contagious itch, ‘infectious itching’. Research into brain activity during itching shows that the same areas are then active as when someone really gets an itch stimulus. So it’s not just something between your ears, it’s really there.’
How did you do this itch test?
‘In the first study, we showed participants different lights on a screen: green, yellow and red. We told one group of participants that they would get less itchy with green light, just as much with yellow and more with red. In this way we aroused expectations. In reality, we constantly gave them the same itch stimulus, it didn’t get any worse or worse. Still, many participants felt that they had less itching with green and more itching with red.’
So we get the creeps from what a researcher says?
‘Not only. Experience also turned out to be important. We had conditioned another group of participants in a learning phase beforehand. They then received a less strong stimulus for green light and a stronger stimulus for red. During the subsequent examination, they still felt less itchy with green and more with red, even though the stimulus was really the same all the time. Having learned the link between the lights and the itch, they still expected it. Especially the combination between that experience and what we told beforehand gave a nocebo effect.’ That is the opposite of the placebo effect: if you expect a negative effect, for example a side effect of a drug, you are more likely to feel worse.
Can you also get rid of itching in the same way?
‘Secure. In the second study, we looked at whether you could also reverse those nocebo effects. You can, if you reverse the expectations. For example, because a doctor outlines a positive pattern of expectations. Or by linking the treatment to something with which the patient has the positive experience of less itching. That way he or she also gets positive expectations.’
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