We have long known that expectations of a malady can be as dangerous as a virus. In the same way that voodoo shamans could harm their victims through the power of suggestion, priming someone to think they are ill can often produce the actual symptoms of a disease. Vomiting, dizziness, headaches, and even death, could be triggered through belief alone. It’s called the “nocebo effect”.

But it is now becoming clear just how easily those dangerous beliefs can spread through gossip and hearsay – with potent effect. It may be the reason why certain houses seem cursed with illness, and why people living near wind turbines report puzzling outbreaks of dizziness, insomnia and vomiting. If you have ever felt “fluey” after a vaccination, believed your cell phone was giving you a headache, or suffered an inexplicable food allergy, you may have also fallen victim to a nocebo jinx. “The nocebo effect shows the brain’s power,” says Dimos Mitsikostas, from Athens Naval Hospital in Greece. “And we cannot fully explain it.”

A killer joke

Doctors have long known that beliefs can be deadly – as demonstrated by a rather nasty student prank that went horribly wrong. The 18th Century Viennese medic, Erich Menninger von Lerchenthal, describes how students at his medical school picked on a much-disliked assistant. Planning to teach him a lesson, they sprung upon him before announcing that he was about to be decapitated. Blindfolding him, they bowed his head onto the chopping block, before dropping a wet cloth on his neck. Convinced it was the kiss of a steel blade, the poor man “died on the spot”.