When Mass Hysteria Goes Viral: Understanding Social Contagion in the Digital Age

In 2019, a disturbing incident in the Malaysian town of Ketereh captured global attention when nearly 40 schoolgirls between the ages of 12 and 18 began screaming uncontrollably, claiming to have seen a “face of pure evil” accompanied by horrific visions of blood and gore. Mental health experts identified this phenomenon as a classic case of mass psychogenic illness—a psychological condition that manifests physical symptoms and spreads socially, similar to how a virus transmits through a population.

This Malaysian incident offers a compelling entry point into understanding how behaviors, beliefs, and even psychological conditions can spread through social networks. While mass psychogenic illness differs from misinformation, both phenomena illuminate how social connections establish pathways of influence that can facilitate the spread of not just physical illnesses, but also mental states and behaviors.

Social networks profoundly shape our perceptions and actions through what researchers call social norms—our understanding of how common or approved certain behaviors are within our peer groups. These perceptions, accurate or not, significantly influence decision-making and behavior adoption.

Unlike viral infections, which may require just one exposure to spread, behaviors typically need multiple contacts to take hold—a concept known as “complex contagion.” This explains why social influence often requires repeated exposure before someone adopts a new behavior or belief.

This process is readily observable in fashion trends. Consider the recent resurgence of baggy jeans. Many millennials initially rejected this return to 1990s fashion, but after multiple exposures through friends or social media, resistance weakens. As one observer put it about similarly questionable Astro Boy Boots on Instagram: “I thought they were ugly at first, but after reading the comments, I guess they’re kind of fire.”

The implications become more serious when examining misinformation on digital platforms. Research demonstrates that false information spreads faster and more widely than accurate information online. By the time fact-checkers mobilize to debunk falsehoods, complex contagion may have already taken hold, with misinformation rapidly proliferating throughout networks.

People spread misinformation for various reasons—sometimes to advance personal agendas, creating echo chambers that filter out contradictory information. Even without malicious intent, many users share falsehoods due to inattention to accuracy or limited digital literacy skills.

Public health researchers and digital platform companies have begun exploring preventative approaches to combat harmful social contagion. One promising strategy is “pre-bunking”—training people to identify and resist misinformation before significant exposure occurs.

Similar to vaccines that build immunity through controlled exposure to weakened pathogens, pre-bunking exposes individuals to mild forms of misinformation while teaching them to recognize manipulation tactics. Google has implemented this concept through online quizzes that help users identify false dichotomies, scapegoating, and slippery-slope arguments—common tactics in misinformation campaigns.

The approach shows promise beyond fighting digital falsehoods. Research suggests pre-bunking can effectively delay harmful behaviors like tobacco use among adolescents. However, like many vaccines, the protective effect diminishes over time without regular “booster” training sessions.

Group-based approaches appear particularly effective at maintaining resistance to harmful social norms. When multiple members of a social network possess strong critical thinking skills, the entire group becomes more resilient against the infiltration of harmful beliefs or behaviors. This concept of “psychological herd immunity” highlights how collective resistance strengthens individual defenses.

Whether combating online falsehoods or helping young people resist peer pressure, evidence supports resistance skills training as an essential tool for safeguarding against harmful social contagion. As our digital and physical social networks become increasingly interconnected, understanding these mechanisms of influence becomes crucial for maintaining both individual and collective wellbeing in an age where ideas—both beneficial and harmful—can spread at unprecedented speed and scale.