(TIME.com) -- We don't think of emotional states as passing from one person to another, but a new study suggests some depressive thoughts can go viral.
Researchers studying a group of college students found that certain types of depressive thinking can spread from close-living roommates like a lingering flu.
Although many people see depression as a chemical imbalance in the brain, scientists say social context and the way you see yourself and the world can be critical in causing and sustaining the illness, which affects around 10% of college-age adults.
"Thinking styles are a really important factor in risk for depression," says the study's lead author Gerald Haeffel, associate professor of clinical psychology at Notre Dame University. "How one thinks about life stress and negative moods is one of the best predictors that we have of future depression."
Haeffel and his colleagues recognized that starting life in a college dorm -- with students transitioning from the familiarity of high school and family and venturing into a completely new social setting -- would serve as an ideal real-world laboratory for studying how social connections and thinking styles of some students can influence others, and how these interactions can affect depression.
"For many freshmen, going to college is a seminal life transition," he says. "They are moving away from home for the first time, and their social context is turned on its head.
"An important feature of our design was that students were randomly assigned to roommates. This means that students were not able to actively choose someone to live with. (They) had to live with a stranger who might have a completely different style of thinking."
Previous research showed that depressive thinking styles tend to become stable and consistent by high school, and that they can increase risk of depression (without necessarily causing the condition) over an entire lifetime.
"Cognitive vulnerability is not the same thing as depression," says Haeffel. "Someone can have a cognitive vulnerability but not appear sad or gloomy. It can be thought of similarly as high blood pressure. High blood pressure is a risk for heart disease, but it does not mean the person has heart disease."
Major life changes, however, like starting college and being exposed to new people, might serve as triggers for whether this risk factor crosses the threshold into becoming an actual depressive disorder, as Haeffel and his colleagues reported in their study, which was published in Clinical Psychological Science.
The authors recruited 108 incoming college freshmen at a private university in the Midwest, including 42 men with male roommates and 66 women with female roommates randomly assigned by the college.
Within their first month of school, the students took an online survey about their thinking styles, stress exposure and depression symptoms. They were surveyed again online three months and six months later.
Haeffel and his team explored two types of thinking previously linked with depression. The first involved rumination or constant brooding about what's going wrong.
"A person who broods will focus on his or her negative mood," says Haeffel. "(They) will think about how sad they feel, try to understand why (they) feel depressed and worry about the implications of their sadness. In contrast, someone who does not brood will tend to distract themselves when feeling sad (for example, by exercising)."
The second depressive style that was examined is known as "hopelessness," which Haeffel says "gets at the self-worth implications and consequences of an event."
For example, a person who feels hopeless might lose a job and see it as a personal failure and a sign that he will never be employable again. A more resilient person might blame the economy or see the situation as an opportunity to get a better position.
The researchers found that hopelessness was not contagious among roommates -- but rumination was.
Hopelessness focuses on the content of one's own thoughts, which are likely deeply embedded and related to other perceptions about the self, and therefore might be less likely to influence the way other people think. Rumination, on the other hand, is a process that is probably easier to mirror by adopting the same focus on negative ideas or attention to sadness, as well as the constant discussion about this darker perspective.
Interestingly, depression symptoms themselves were not contagious: simply having a roommate with symptoms of the disorder did not increase risk of developing the mental illness.
But those who picked up a ruminative style of thinking from their roommates during the first three months of school had more than double the number of depressive symptoms of those who either weren't exposed to this perspective or didn't adopt the rumination three months later. And the risk was magnified if they experienced high levels of stress.
The study also found, however, that healthy thinking was also contagious. "Those assigned to a roommate with a more positive thinking style developed a more positive style themselves whereas those assigned to a roommate with a negative style became more negative," Haeffel says. The study could not determine what made a particular roommate's style more likely to dominate and influence, rather than be influenced.
Such information could enhance the current findings and contribute to new ways of treating and preventing depression. The results suggest that depressive thinking styles can still be influenced during young adulthood -- so this risk factor can be minimized even if it has already developed during high school or earlier. Targeting ruminative thinking might also enhance therapy.
"The therapist could assess if people in the patient's life are modeling and providing adaptive cognitive feedback about stress and negative life events," says Haeffel. "The therapist could then provide those with negative thinking styles with information about the contagion effect along with training that would help them identify negative thought patterns and provide examples of more adaptive ways of thinking."
So while depressive thoughts can spread from person to person, making depression more contagious than previously thought, these perspectives can also be the focus of effective therapies that could, just as antiviral and antibacterial agents do, block them from taking hold.
This article was initially published on TIME.com.