The evacuation of Heathrow’s Terminal 4, initially attributed by police to a probable case of “mass hysteria” (or mass psychogenic disorder), provides a stark example of how social contagion operates. This phenomenon describes the rapid, seemingly infectious spread of symptoms or behaviors within a social group, even in the absence of a physical infectious agent. While the symptoms experienced—such as nausea or breathing difficulties—are real to the sufferers, the trigger is purely psychological, often exacerbated by background anxiety, stress, and the powerful mechanism of a positive feedback loop.
Understanding Mass Psychogenic Disorder
Mass hysteria is a form of social contagion where clusters of illness or symptoms spread through a community with no discernible medical or toxic cause. These symptoms, which can include headaches, dizziness, or even convulsive fits, are nevertheless real for the people experiencing them, originating from psychological factors rather than a physical illness.
Historical examples abound, from the “dancing plague” of 1518 in Strasbourg to outbreaks of twitching in 19th-century nuns. Sociological analyses of past events—such as a 1962 outbreak of illness at a factory—suggest that the main predictors for such contagions are pre-existing anxiety and stress within the affected social group. When a stressful environment is combined with an initial trigger, the stage is set for a psychological epidemic.
The Positive Feedback Loop Mechanism
Social contagion follows the same mathematical mechanism as an infectious disease: a positive feedback loop.
This mechanism can be visualized as a snowball effect: a small initial incident (like one person feeling unwell) starts to gather size and pace as it spreads. In the Heathrow incident, 21 people were treated by ambulance staff, with the Metropolitan Police suggesting the incident “snowballed” from a single person falling ill. The infectious element in social contagion is emotion and idea, not a virus. One person’s fear or anxiety, fueled by an ambiguous situation (like a public evacuation), triggers a similar response in those around them. The collective panic then validates the initial fear, making the next person even more susceptible.
The Perils of Viral Ideas in the Digital Age
While the situation at Heathrow was quickly resolved (though an update later reported the finding of a CS canister, complicating the initial “mass hysteria” conclusion), the principle remains: ideas and emotions can spread like diseases, and they are often much harder to stop than actual germs.
The advent of the digital age has significantly amplified this risk. Social media can act as a high-speed vector for the viral spread of fear, falsehoods, and pervasive myths. The speed and reach of these “social epidemics” mean they can reach a critical mass in virtually no time, making them extremely difficult for authorities to counter with facts. Underestimating the potency and longevity of a contagious idea—its ability to enthrall a group—can lead to severe misjudgments in how authorities or the public understand and respond to a rapidly unfolding situation. The risk, as sociologists warn, is that our interconnected world makes us more vulnerable to mass hysteria than ever before.
