In 2021, neurologists across the United States, United Kingdom, Germany, Canada, Denmark, and France began seeing a surge of teenagers — predominantly girls, median age around 18 — presenting with explosive-onset tic-like movements and vocalizations that resembled Tourette syndrome. The symptoms appeared abruptly rather than gradually. They were overwhelmingly complex (full-body jerks, coprolalia, bizarre stereotyped phrases) rather than the simple eye blinks and throat-clearing that characterize early Tourette’s. They didn’t wax and wane the way tics do. And when clinicians asked the patients what they’d been doing before the symptoms started, the answer was consistent: watching TikTok.
Researchers at Hannover Medical School in Germany identified the specific trigger. A 22-year-old German YouTuber named Jan Zimmermann, who runs a channel called Gewitter im Kopf (“Thunderstorm in the Brain”), had been posting videos of what he claimed were his Tourette symptoms. The channel became the second most successful YouTube channel in Germany. Clinicians determined that while Zimmermann likely had mild actual Tourette syndrome, the majority of his on-camera behaviors were functional — not tics. Teenagers watching the videos developed symptoms that overlapped specifically with the behaviors Zimmermann displayed on camera. The symptoms weren’t random. They were modeled — unconsciously reproduced from a virtual index case that the patients had never met in person, had never shared a room with, and had encountered only through a screen.
The researchers named the phenomenon Mass Social Media-Induced Illness — MSMI — and published it in Brain, one of the oldest and most respected neurology journals. It was the first documented outbreak of mass psychogenic illness spread entirely through social media, without any physical proximity between the affected individuals. The condition that has existed for at least 600 years had found a new transmission vector.
The mechanism: how groups generate symptoms
Mass psychogenic illness — historically called mass hysteria, now more precisely termed mass sociogenic illness — involves the spread of physical symptoms through a population in the absence of any infectious agent, toxin, or organic cause. The symptoms are real. The suffering is genuine. The mechanism is psychological: emotional contagion, suggestibility, and the unconscious modeling of observed symptoms, amplified by stress, anxiety, and social cohesion within the affected group.
The pattern is remarkably consistent across centuries. An outbreak typically begins with a single person — the index case — who develops symptoms in a stressful environment. Other people who are socially connected to the index case, or who learn about the symptoms through communication, begin experiencing similar symptoms. The spread follows social networks, not transmission pathways. It usually begins among people of higher social status within the group and expands outward. Media coverage amplifies and perpetuates outbreaks. And the symptoms, while they lack organic cause, are not fabricated — the people experiencing them cannot simply choose to stop.
The TikTok tic outbreak is diagnostically distinguishable from actual Tourette syndrome on multiple clinical criteria. In the MSMI patients, onset was abrupt rather than gradual. Symptoms constantly deteriorated rather than following the waxing and waning pattern of tics. Simple movements like eye blinking were absent or rare — the symptoms were overwhelmingly complex and theatrical. Movements were primarily in the arms and trunk rather than the face and eyes. Premonitory urges — the sensation that precedes a tic in Tourette syndrome — were either absent or described with atypical qualities. And nearly all patients had pre-existing psychiatric conditions: 81 percent showed abnormalities in social behavior, 47 percent had obsessive-compulsive behaviors, 41 percent had anxiety, and 31 percent had depression. Psychological stressors — including the pandemic lockdown, social isolation, and family disruption — were identified in every case.
Havana syndrome: mass psychogenic illness in the intelligence community
In late 2016, U.S. diplomats and CIA personnel stationed in Cuba began reporting neurological symptoms — dizziness, headaches, hearing loss, difficulty concentrating, fatigue, memory problems — that they attributed to exposure to mysterious sounds around their homes and offices. The condition spread to personnel in other countries including China, Austria, and the United States itself. Over 1,000 people eventually reported symptoms. The U.S. government labeled the cases “anomalous health incidents” and spent years investigating potential causes including microwave weapons, directed-energy devices, and sonic attacks.
In 2024, NIH studies published in JAMA examined 86 people with reported Havana syndrome. The results showed no clinical signs or brain image abnormalities to explain the symptoms. The only significant differences between affected personnel and matched controls were self-reported fatigue, stress, and depression. A 2023 intelligence community assessment concluded that the injuries were not the result of foreign attacks, pointing instead to previous injuries, stress, environmental factors, and “social factors” — group psychology in which symptoms reported by one individual spread serially through a community.
The FBI’s Behavioral Analysis Unit had reached the same conclusion in 2018: mass psychogenic illness. The finding was classified. Recordings of mysterious sounds that victims said coincided with their attacks were analyzed and identified as the mating calls of the Indies short-tailed cricket. Medical sociologist Robert Bartholomew, co-author of a book on the subject, described the outbreak as following the textbook pattern: it began among a small, cohesive group of high-status individuals in a stressful environment, then spread through their social network, amplified by media coverage and institutional attention.
The political dimension made the diagnosis almost impossible to deliver. Telling CIA officers that their debilitating symptoms are psychogenic — real but psychological in origin — is functionally equivalent to telling them their suffering isn’t legitimate, which it is. The stigma attached to psychogenic illness created a vacuum that alternative explanations (energy weapons, foreign attacks) filled, which in turn attracted congressional hearings, diplomatic consequences, and further media coverage that perpetuated the outbreak. The condition persisted in part because the correct diagnosis was politically unacceptable.
The pattern across centuries
The TikTok tics and Havana syndrome are the 21st century’s most prominent outbreaks, but the phenomenon is old enough to have its own medieval literature. The dancing plagues of the Middle Ages — most notably Strasbourg in 1518, where hundreds of people danced uncontrollably in the streets for days — are the earliest well-documented cases. Nuns in convents experienced outbreaks of involuntary meowing, biting, and convulsions throughout the 15th and 16th centuries. The Salem witch trials of 1692 featured young girls exhibiting fits, contortions, and screaming that were attributed to demonic possession — symptoms that fit the pattern of mass psychogenic illness in a small, stressed, theocratic community.
In 2011, students at Le Roy Junior-Senior High School in upstate New York developed symptoms resembling Tourette syndrome. Environmental causes were investigated and ruled out. The students were diagnosed with conversion disorder and mass psychogenic illness. In Sweden, refugee children facing deportation developed resignation syndrome — coma-like states lasting weeks or months — a condition that appears to exist exclusively among the refugee population in Sweden and is believed to involve psychological contagion among young people in similar circumstances.
What social media changed
Until the TikTok outbreak, every documented case of mass psychogenic illness required physical proximity. People had to be in the same school, factory, convent, embassy, or community. The spread followed face-to-face social networks. The German researchers’ designation of MSMI as a new category of mass psychogenic illness reflects the structural break: for the first time, the index case was virtual. The affected teenagers had never met Jan Zimmermann. They encountered his symptoms through a screen. The emotional contagion that drives the phenomenon — identification with the index case, modeling of observed behaviors, amplification through stress and anxiety — operated across a digital medium rather than a physical one.
The implications are straightforward and alarming. Physical proximity imposed a natural limit on outbreaks. A school has a few hundred students. A convent has a few dozen nuns. An embassy has a few hundred staff. TikTok has over a billion users. The transmission vector that social media provides is orders of magnitude larger than any physical social network. Zimmermann’s channel had millions of subscribers. Tourette syndrome content on TikTok accumulated billions of views. The potential population of susceptible individuals exposed to modeling stimuli expanded from the hundreds (in a physical-proximity outbreak) to the hundreds of millions.
The German researchers found that the sex ratio of affected patients correlated with the sex of the index case: in Germany, where the index case (Zimmermann) was male, roughly half the patients were male. In English-speaking countries, where the most influential Tourette content creator was female, patients were predominantly female. The identification mechanism — emotional connection to the index case — was specific enough to follow demographic alignment between the model and the affected population.
Treatment that worked included reducing social media exposure (specifically tic-disorder content), cognitive behavioral therapy, stress management, and reassurance about the functional nature of the symptoms. Medications used for actual Tourette syndrome were largely ineffective, which is itself a diagnostic criterion: functional tics don’t respond to the pharmacology that works on neurological tics because the mechanism is different.
The condition researchers described in Brain is the 21st-century expression of a phenomenon that has existed for as long as humans have lived in groups: the capacity of social networks to generate real physical symptoms through psychological contagion. What changed isn’t the mechanism. It’s the scale. The convent had walls. TikTok doesn’t.
We cover mass psychogenic illness alongside ball lightning, the Hum, UAPs, and the full landscape of phenomena that exist at the boundary between the explained and the unexplained across our Fortean Phenomena course — including why the oldest psychiatric phenomenon in recorded history found its most powerful transmission vector in an app designed for dance videos.