Painting of a dancing mania by Pieter Breughel.Pieter Breughel/ Wikimedia Commons

In June 1962, 62 workers at an American textile factory fell ill with symptoms including numbness, nausea, dizziness and vomiting. Of these 62 workers, 59 were women. Many of the workers believed they had been bitten by insects that had arrived in a recent fabric shipment. Entomologists and other scientists were called in to find the cause of the rapidly spreading illness. However, none was found. This peculiar event was later dubbed the June Bug.

A few years later, on 7th October 1965, in a girls school in Blackburn, England, several students started to complain of dizziness. Soon after, some students started fainting and others presented with moaning, chattering teeth, hyperpnea (increased rate and depth of breathing) and tetany (involuntary muscle contractions). Within just a few hours, 85 girls had to be rushed to hospital. Once again, no cause for the symptoms was determined.

These mysterious cases are two examples of what is referred to as mass sociogenic illness, mass psychogenic illness (MPI) or mass hysteria.

Mass sociogenic illnesses are defined as the rapid spread of illness symptoms through a population where there is no viral or bacterial agent responsible for the contagion. However, despite the lack of a perceivable infectious agent, these illnesses can cause severe physical symptoms and potentially lead to hospitalisation.

“It is clear that stress levels play an important role in susceptibility to mass sociogenic illnesses.”

These illnesses are far from a recent phenomenon, with the earliest studied cases being the dancing manias of the Middle Ages. During these manias, observers documented that afflicted individuals would go into trance-like states, in which they would dance in large groups for extended periods of time, sometimes even weeks.

Similarly, between the 15th and 19th centuries, reports surfaced of an “epidemic” that was sweeping nunneries. Afflicted nuns would start behaving in what was described as “rebellious” ways, such as using foul and blasphemous language, and engaging in suggestive behaviours. Both these illnesses were thought to have been brought on by demonic possession.

It is still poorly understood how and why mass sociogenic illnesses occur. However, it is theorised that these illnesses are physical manifestations of anxiety, often caused by what are perceived to be a credible threats.

This explanation may help us understand the well-documented shift in the presentation of these illnesses before and after the 20th century. Prior to the 20th century, mass sociogenic illnesses were largely seen as signs of demonic possession and often presented as “motor hysterias” with individuals experiencing convulsions, contractures, tremors and paralysis. However, since the 20th century, most documented mass sociogenic illnesses were initially presumed to be the result of chemical or biological agents, such as an infectious pathogen or a toxic gas in the environment. In most cases, individuals presented with breathlessness, nausea, headaches, dizziness and weakness.

“Would the mass sociogenic illnesses of the past even be considered “illnesses” in today’s society?”

Further information can be gleaned by looking at the groups that tend to be affected. It is clear that stress levels play an important role in susceptibility to mass sociogenic illnesses. For example, research into the June Bug outbreak found that those affected were more likely to work overtime frequently and to provide the majority of their family’s income. These individuals were also more likely to deny their difficulties, indicating they were individuals who did not deal with stress effectively. Similarly, some researchers believe women may be more prone as they are typically exposed to more stressful situations.

These illnesses also appear to be more common in groups that are strictly religious. A recent example was seen in a girls school in Kelantan, Malaysia in August 2019, where many students started screaming and claiming to have seen “a face of pure evil”. It is interesting to note the similarities between this example in Kelantan, one of the most religiously orthodox Malaysian states, and the “demonic possessions” of the past, perhaps revealing a trend in how such illnesses present in deeply religious societies.

In this respect, the changing attitudes of society and medicine greatly impact our perception of mass sociogenic illnesses, as our perception of what is “normal” and what is an “illness” evolve. Notably, accounts of the mass sociogenic illnesses of the past are laden with judgement, such as the description of nuns behaving in “rebellious ways” and making “obscene gestures”. Such judgements beg the question: would the mass sociogenic illnesses of the past even be considered “illnesses” in today’s society?


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In the midst of the COVID-19 pandemic, further questions have been raised about how mass sociogenic illness may complicate the epidemiological picture of a pandemic. The widespread fear and anxiety that have arisen during the pandemic mirror that of mass sociogenic illness. These sentiments have only been exacerbated by how quickly the virus has spread, the implementation of quarantine measures in many countries, and the continuous media coverage of the pandemic.

In July, the Joint Biosecurity Centre (JBC), a government body set up to inform decisions on tackling COVID-19, announced it would be alert to local episodes of mass sociogenic illnesses, where people within a community experience COVID-19 symptoms without an underlying viral cause. The JBC raised concerns that, in addition to complicating the epidemiological picture of the pandemic, these local outbreaks might cause “substantial anxiety, anger and loss of trust in the community” if poorly handled.

In an age where the intersection between mental and physical health is increasingly appreciated, it is important that we regard mass sociogenic illnesses not as curious tales of the past, but rather as evidence of the importance of a holistic approach to medicine.