Imagine the following scene. An 18-year-old college freshman, Rose, calls her parents at the end of her first semester away at school:Mom: “Honey, how are you? How are classes going?”Rose: “Ahh… Well, I caught something from Jen, my roommate.”Dad: “Like a cold, honey? What did you catch?”Rose: “Not a cold, dad, something worse.”Mom: “Something worse?! What, honey, what happened to you?”Rose: “I caught a cognitive vulnerability to depression.”Dad and Mom in unison: “A what?!”Dad: “Depression isn’t something you catch, honey. I’m so glad you don’t have the flu.”Rose: “No dad, it’s for real. I can tell. I caught her cognitive vulnerability. I know it, and now I’ll never finish the semester…”Sounds wild, right? Well, new research from the University of Notre Dame found that a so-called cognitive vulnerability to depression is, indeed, contagious among college roommates. Rose’s roommate’s vulnerability to depression has “rubbed off” on her, and now she’s becoming stuck in the thick of depressive fog—persistent sadness, loss of pleasure, low energy, trouble sleeping, etc.MORE: How to Get out of a Toxic RelationshipWhat is a cognitive vulnerability (CV) to depression? CVs are thought of as psychological risk factors that predispose people to become depressed, especially when we are confronted with a stressful life event (i.e., moving away to college, illness or divorce). CVs describe characteristic styles of thinking that people use to understand their experiences. One of the CVs studied in this research was psychological rumination, or the tendency to regularly reflect on how bad you feel, why you feel as you do, and, in general, to brood about bad moods. If you’re a person with the tendency to ruminate—to get up in your head, and to think over and over again about how awful you feel and why you are so down—you’re much more likely to become clinically depressed when you face difficult experiences.In the Notre Dame study, the researchers assessed changes in a person’s rumination compared to her prior rumination scores, and as a function of her roommate’s prior rumination scores. Their results revealed that how a person thinks about the world is associated not only with what’s happening inside her own head, but also with what’s happening inside her roommate’s head.QUIZ: How Happy Are You?People who were randomly paired with a roommate having a high CV to depression demonstrated increases in their own CV over time. In the case of the tendency to ruminate, this increase was observed within the first three months of college! Furthermore, increases in CVs to depression—remember, this is the risk factor—were associated with increases in actual depressed moods six months after starting college.QUIZ: Test Your Close RelationshipsYou don’t need to be a psychologist to understand how this contagion process might work—and you don’t have to be in college to see its effect. We’ve all felt it before: We tend to feel depressed when we’re around depressed people. But psychologists generally think of CVs for depression as something fairly stable or immutable, sort of the way people think about genetic risk (If you have it, you have it; if you don’t, you don’t). This is why showing that the CVs themselves are contagious is a profound revelation. We don’t simply catch the low mood—we catch the vulnerability to become depressed in the future.The long-term effects of “catching” the rumination CV are not yet clear. If you’re a pretty happy person and spend a lot of your time with a high ruminator, what does this mean for your likelihood to become depressed in the future? We just don’t know yet.MORE: How to Stop Racing ThoughtsAlthough the results of this study sound ominous, there is a way to look at this work from an entirely different perspective. This study is correlational, and that means you can interpret the cross-roommate correlation in two ways. First, as we’ve done here: High CV in one person predicts high future CV in the other person. Alternatively, it is equally accurate to say low CV in one person predicts low future CV in the other person. In other words, to the extent that these processes are causal, we can be protected from developing a vulnerability to depression by being paired with someone who does not have a tendency to ruminate or to see hopelessness all around them.This research is excellent because it has zoomed deeply into an important dynamic that can recast how we think about risk for depression. In real life, we are surrounded by people all the time, and how are we to know what we’re catching from one person versus another person?RESEARCH: “Fat Talk” Is ContagiousI suggest we treat this new information about CV contagion in a manner akin to how we think about preventing the flu or common cold. Take all the precautions you can. Sometimes, it’s unavoidable to be around someone with a cold. You wash your hands as much as possible, minimize contact with sick people, etc., etc. When we think about the CVs for depression, the same should be true. Sometimes you can avoid being around a high ruminator. Sometimes you can’t. (You might be that person yourself!) We should seek to offset these exposures by also surrounding ourselves (both physically and digitally) with people that look on the bright side, that see the good in the world and that help us maintain our positive spirits.