What Caused the Dancing Plague of 1518?

Background

In July 1518, a woman remembered in period records as Frau Troffea began dancing in a street in Strasbourg, then a city within the Holy Roman Empire. Within about a week several dozen others had joined her, and within a month contemporary accounts describe as many as 400 people dancing, many seemingly unable to stop of their own will. Physicians of the city, working from the era's humoral medical theory, diagnosed the afflicted with "hot blood" that needed to be danced out rather than suppressed, and city authorities responded by clearing a guildhall and grain market, building a wooden stage, and hiring musicians to keep the dancing going under supervision.

That response, modern historians generally agree, appears to have worsened rather than resolved the outbreak: participants continued dancing for days, and period records describe a number collapsing from exhaustion and some reportedly dying, attributed at the time to stroke or heart attack brought on by continuous movement. Only after the encouragement approach failed did city officials change course, transporting the afflicted to a mountain shrine associated with Saint Vitus at nearby Saverne, where a religious ritual was performed said to have ended their compulsion to dance.

Main Theories

The mass psychogenic illness explanation

The explanation most fully developed in modern scholarship, argued at length by historian John Waller in his 2008 book A Time to Dance, A Time to Die, holds that the 1518 outbreak was a form of mass psychogenic illness: a genuine, involuntary physical and psychological affliction with no organic disease cause, triggered by extreme collective stress and spread through social and psychological contagion among people who shared the same cultural framework. Waller documented that the region around Strasbourg had suffered severe famine, smallpox, syphilis, and broader economic hardship in the years immediately before 1518, and that local folk belief already held that Saint Vitus could curse offenders with compulsive dancing, giving susceptible individuals both the psychological stress and the specific cultural template the episode took.

This account draws on a documented, recognised modern psychiatric category, mass psychogenic illness, observed in other stress-linked outbreaks of shared involuntary behaviour across different cultures and eras, and it accounts well for features unique to the 1518 case: the outbreak's concentration in a specific, recently traumatised population, its spread through social proximity, and its resolution once participants were removed to a setting, the Saint Vitus shrine, consistent with the era's own belief about the affliction's cause and cure.

The convulsive ergotism hypothesis

An older explanation, once widely repeated, attributes the dancing plague to convulsive ergotism, poisoning caused by Claviceps purpurea, a fungus that can contaminate rye and produces alkaloids with effects including hallucinations and involuntary muscle spasms. The hypothesis draws on the fact that ergot contamination was a real and recurring hazard in medieval European rye-growing regions, and that ergotism had genuinely been linked to other unusual behavioural outbreaks historically.

Historians, including Waller, argue the hypothesis fits the 1518 case poorly. Convulsive ergotism typically produces uncoordinated, involuntary spasms, along with other symptoms including gangrene from the toxin's effect on blood circulation, none of which matches the sustained, rhythmic, coordinated dancing that contemporary accounts describe continuing for days. The absence of reported gangrene or other classic ergotism symptoms in the Strasbourg records, combined with dancing's incompatibility with the kind of muscle spasms ergotism actually produces, is treated by most current historians as sufficient to discount the hypothesis for this specific episode, even though ergot poisoning remains a genuine and separately documented medieval health hazard.

Common Misconceptions

The most common error is treating the dancing plague as a single unexplained mystery rather than a documented event with a well-supported, if not absolutely certain, modern explanation. The historical record of what happened, the dancing, the civic response, the deaths, and the eventual resolution at Saint Vitus's shrine, is unusually well documented for a 16th-century event, drawn from multiple independent physician and civic sources; what remains open is the precise psychological mechanism, not whether the episode occurred.

It is also often assumed the ergotism hypothesis remains the mainstream explanation, since it circulated widely in earlier popular accounts. Current historical scholarship has largely moved away from it for this specific outbreak in favour of the mass psychogenic illness explanation, precisely because the physical symptoms ergotism produces do not match the sustained, coordinated dancing period sources describe.

Current Consensus

Historians of medicine and the period generally accept that the 1518 Strasbourg dancing plague was a real, documented event involving genuine involuntary behaviour by a substantial number of people, not a later legend or exaggeration, and that mass psychogenic illness, triggered by acute regional stress and shaped by an existing local belief in Saint Vitus's curse, is the best-supported explanation available. The convulsive ergotism hypothesis is treated as inconsistent with the specific symptoms recorded.

What remains genuinely open is a matter of degree rather than kind: the precise psychological and social mechanisms by which mass psychogenic illness spreads and sustains itself over weeks, in this case and others, remain an active area of research in psychiatry and medical history, rather than a fully settled question.

Why This Mystery Endures

The dancing plague endures partly because its central image, dozens of people dancing uncontrollably in the streets until some of them died, is vivid enough to resist a mundane explanation even once one exists, and partly because the mundane explanation, mass psychogenic illness, is itself a genuinely strange feature of human psychology that most readers encounter for the first time through this case. Unlike many entries in this site's coverage, the dancing plague is not really a live evidentiary dispute; it endures as a story because the true explanation is nearly as unsettling as the folk one it replaced.

The episode also sits naturally alongside the Serbian vampire panics of the following two centuries: both are real, officially documented collective panics in early modern Europe, met at the time with the available medical and religious frameworks of their day, and both were eventually given evidence-based explanations, disease and decomposition science for the vampire panics, psychogenic illness for the dancing plague, that replaced supernatural readings without requiring anyone involved to have been lying. Read together, the two cases show the same underlying pattern this site traces repeatedly: a real, frightening, collectively witnessed event, explained at the time through the only framework available, and only much later reframed through evidence its original witnesses had no access to. Peter Stumpp's 1589 werewolf trial, a generation later and a different country, shows the same pattern applied through a judicial rather than a medical lens: a real pattern of violence, processed through the era's own available framework.