We don’t often think mental health is contagious in the same way a virus is. But a depressed person in a family can cause that depression to spread through the family, and an anxious person in a lift can be felt by the others. We humans are mimics, argues Don Forsyth, and we need to catch psychological problems early, so that they don’t spread further than they need to. 

In 2011 millions of citizens of Tunisia protested government authority and repression. The movement spread to adjoining countries, sparking the Arab Spring. Fewer than 10% of US households had microwave ovens in 1978; ten years later they were in nine out of 10 kitchens. On a warm day in June one worker after another fell sick, complaining of nausea, headaches, and dizziness. Rumors circulated about “some kind of bug” that had infested a recent shipment of cloth from overseas, but no bug was ever found. Dozens of injuries resulted when the TikTok Skullbreaker challenge (sweeping a person's legs out from under them) went viral. As SARS-Covid-19 spread around the world, so did resistance to recommended safeguards, suspicions about the source of the virus, and distrust in health authorities.

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Diseases aren't the only things that are contagious. Think about how contagious laughter can be. When one person starts laughing, it's often not long before others join in. The same goes for enthusiasm. Work teams with energetic, consistently enthusiastic leaders brim with esprit de corps, but morose leaders make for morose teams. Countries differ in their level of collective mood, so when people immigrate, so do their moods: when people move to countries with higher levels of happiness, they themselves become happier.

But, just as a good mood, enthusiasm, and happiness can spread from one person to another, so can depression, stress, and anxiety. A folie a deux, or "madness of two," occurs when the delusional beliefs or mood disturbances of one person in a close relationship are transferred to their partner in that relationship. Suicides sometimes occur in clusters; media reports of the suicide of celebrities, for example, trigger an increase in suicide attempts and suicides. College students gradually become increasingly depressed over the course of the academic year if they are randomly assigned to share a dorm room with someone who is depressed. People, when gathered in crowds, sometimes suddenly panic when a sense of dread and disaster permeate the group. Even delusions can be infectious.  If your close associates believe in lizard people, a flat earth, or 5G chips in Covid-19 vaccines, there is a good chance that you will eventually come to believe these unlikely notions, too.

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Without realizing it, we often do what others do—we are natural mimics.

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Experts and laypersons alike have always been fascinated by the tendency for behaviors, thoughts, and feelings to spread from one person to another. Over a century ago the French physician Gustave Le Bon argued that when people gathered in certain circumstances, such as periods of intense anxiety, uncertainty, and external threat, bizarre thoughts and actions become contagious: they spread through a group, for emotions and behaviors could be transmitted from one person to another just as germs can be passed along. Subsequent researchers used terms like “collective psychosis,” “mass contagion,” “psychogenic delusions,” and “mob mentality” to emphasize the strange and psychologically dangerous side of social contagion.

But in hindsight, social contagion is not so extraordinary that it requires an extraordinary explanation. We humans are a highly social species, so our connections to other people are plentiful, robust, and influential. In consequence, our thoughts, actions, and emotions--and that includes our mental health and well-being--depend, in part, on other people. Without realizing it, we often do what others do—we are natural mimics. But when others around us display anger, nervousness, sadness, or anxiety, we ourselves may act and feel angry, nervous, sad, and anxious. Our capacity for empathy allows us to respond to the suffering of others, but when we console a friend in distress the empathy producing circuits in our brains mirror their emotions; their sadness, anxiety, or tension can become our sadness, anxiety, and tension. Other people are also a vitally important source of information, but the data they provide is not always accurate, unbiased, helpful, or health-promoting. Because much of our learning is social in source—gained from people around us—the paranoid partner, the depressed friend, and the critical parent can convince us that someone is out to get us, that things are hopeless, and that we have low worth as a person. And even though we can resist social pressure, we often unwittingly follow the crowd and do what others are doing. When nearly everyone in your sorority has an eating disorder or your friends all drink unhealthy amounts of alcohol to deal with social pressures, before long you, too, will fall in line and conform to the group’s norms.

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In consequence, to call deleterious psychological conditions such as anxiety and depression contagious is to speak metaphorically. Actions, emotions, and ideas don’t flow from one person to another through some odd as-yet undiscovered psychological mechanism, but through such quotidian social processes as mimicry, empathy, conformity, social learning, and influence. Moreover, these processes are very different from those that cause physical illnesses to be contagious. With the flu, STDs, and Covid-19, viruses or bacteria are passed from one person to another by direct and indirect contact with the pathogen. But, in cases of social contagion, the condition is passed through routine social interaction. Depression and anxiety are “socially transmissible conditions” (STCs), but their means of transmission are very different from the processes that cause contagious physical illnesses.

These differences have implications for the design of safeguards and interventions for sustaining and promoting mental health. What can be done, for example, to prevent the spread of depression or the flow of anxiety in a family, an organization, a school, or a community? Commonly accepted means of limiting the transmission of contagious physical illnesses, such as quarantine, vaccination, and contract-tracing, may be effective, but some may not be. Isolation, for example, is not a viable option. Depression and suicidal ideation only intensify when people keep their problems private, so people experiencing depression need to share their thoughts and feelings with other people. Isolation would put them at great risk. Quarantine would not work, either, for it would require isolating people who are connected, socially, to a person with depression, even though they are not evidencing any symptoms of depression themselves. Inoculation is not yet feasible given the uncertain effectiveness of pharmaceutical treatments and their known side-effects—there is no anti-depression vaccine.

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Devoting more resources to the early identification of psychological problems, and responding to initial cases quickly—a recommended best-practice when dealing with physical contagions—seems more reasonable

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Other approaches hold more promise. Wearing a mask—a highly recommended safeguard to prevent the spread of Covid-19—might work to prevent social contagion as well, but only because people keep their distance, psychologically and physically, when they are masked. However, devoting more resources to the early identification of psychological problems, and responding to initial cases quickly—a recommended best-practice when dealing with physical contagions—seems more reasonable. Early intervention could even include contact tracing provided people’s privacy is respected and no one is left feeling like a Typhoid Mary.

Public education, too, is needed to ensure that the social bases of psychological problems, and their potential transmissibility, are better understood. Before the widespread acceptance of the germ theory of illness, people did not take even basic precautions, such as washing hands or sanitizing surfaces, because they simply did not know how illnesses were transmitted. Germs and viruses are normally invisible, so we did not recognize them as causes of illness and disease. Similarly, the social processes that sustain social contagion, such as social mimicry and normative influence, are more often unseen rather than scrutinized. Caught up in the relentless flow of social interaction, we do not realize how others are influencing us, and how we are influencing them. But when people learn more about the causes of psychological conditions such as depression and how they can “catch” them from others, they can take steps to protect themselves and the people around them. The Covid-19 pandemic taught us act in ways that would limit our exposure to the virus and be mindful of the health of those we come into contact with. Similarly, let’s hope that a world-wide epidemic of psychological suffering won’t be needed to teach us to act ways that not only bolster our own psychological health and well-being, but also the psychological health and well-being of those around us.