Many illnesses are contagious. You'd do well to avoid your neighbor's sneeze, for example, and to wash your hands after tending to your sick child.
But what about mental illness?
The idea that anxiety, autism or major depression could be transmitted through contact may sound crazy — and it probably is. There's a lot we don't know about the origins of mental illness, but the mechanisms identified so far point in other directions.
Nonetheless, we do know that people's emotions can be affected by the emotions of those around them — a phenomenon known as "emotional contagion" — and that specific symptoms of mental disorders, such as binge eating, can sometimes spread among peers. We also know that many people hold scientifically unfounded views about transmission. For instance, some people believe that organ transplant recipients can acquire the personal characteristics of their donors, a view for which there's no serious scientific support.
So, could it be that some people believe psychiatric disorders can be contagious? And, if so, does this belief have consequences for their willingness to interact with people diagnosed with those disorders?
A recent paper by Jessecae Marsh and Lindzi Shanks, published in the journal Memory & Cognition, suggests the answers are "yes" and "yes." Many of their participants agreed that mental disorders can be communicated from one person to another, and individuals' views about the communicability of a disorder strongly predicted their willingness to interact with a person having that disorder.
In their first study, Marsh and Shanks had 45 undergraduate participants answer questions about 12 different mental disorders that ranged from alcohol abuse and ADD (attention deficit disorder) to schizophrenia and generalized anxiety disorder. For each one, participants were asked to rate how likely they thought it would be for someone to catch the disorder through close contact with a person who had it, with ratings on a scale from zero percent probability to 100 percent probability.
Ratings varied strongly across disorders, with the highest average estimated transmission rates for alcohol abuse (56 percent), anorexia (35.7 percent), major depressive disorder (32.2 percent) and hypochondria (30.6 percent). The disorders with the lowest estimated transmission rates were Tourette's disorder (4.2 percent), autism (5.3 percent), schizophrenia (7.4 percent) and bipolar disorder (11.2 percent).
Participants answered a variety of additional questions, including how willing they would be to interact with someone with each disorder. For example, they rated their agreement with statements like, "I would be willing to work with a person with anorexia," or "I think someone with schizophrenia is dangerous."
The study's central result was this: People's willingness to interact with someone with a given disorder was best predicted by their belief about the communicability of that disorder, with other beliefs — about, for instance, the disorder's psychological basis and the extent to which an individual can control the symptoms she displays — playing a much smaller role. A second experiment helped establish that this predictive relationship was actually causal: It was indeed beliefs about communicability that caused different attitudes toward personal interaction.
But how, exactly, did people think the transmission of mental illness from one person to another actually occurred?
A follow-up study with 122 undergraduates probed more deeply into people's beliefs about the mechanisms involved. Diseases like chicken pox and the flu were overwhelmingly thought to be transmitted through physical contact on a relatively short timescale (e.g., being sneezed on or touching the same object). But the most common mechanisms of transmission for mental illness involved social interactions and were generally believed to operate on a much longer timescale — closer to years than to minutes.
Not surprisingly, though, the responses participants provided were pretty light on specifics. For instance, one participant explained that generalized anxiety disorder can be transmitted because "the person's anxiety will rub off." For alcohol abuse, a participant explained: "If you hang out with someone that drinks all the time, you will soon be drinking a lot as well."
People who suffer from mental illness face a variety of challenges, often including stigma and social isolation. The findings from these new studies help identify one factor that may contribute to both: people's beliefs about the transmission of mental illness from one person to another.
The thing is, these beliefs about transmission are almost certainly false. This may seem disheartening, but it also makes room for a sliver of hope: the hope that a small bit of education could go a long way.
Tania Lombrozo is a psychology professor at the University of California, Berkeley. She writes about psychology, cognitive science and philosophy, with occasional forays into parenting and veganism. You can keep up with more of what she is thinking on Twitter: @TaniaLombrozo