Happiness is contagious, a new study suggests, but depression isn’t. New research from the Universities of Warwick and Manchester suggests that being around positive friends can help people recover from depression — and help prevent it from taking hold in the first place.

According to the World Health Organization, depression affects more than 350 million people globally, making it one of the world’s biggest public health concerns. Understanding the social processes that drive depression, the researchers write, is key to figuring out how to treat and prevent it.

Looking at data on depression from more than 2,000 American adolescents, the researchers modeled the spread of mood within social networks in the same way they’d track an infectious disease. They found that depression doesn’t spread, but that healthy, positive moods do. The research shows that, for adolescents, being around happier friends cut the probability of developing depression by half over a six- to 12-month period, and doubled their chances of recovery.

It makes intuitive sense that depression isn’t “contagious” because depressed individuals have a tendency to withdraw and thus exert less influence on their circle of friends, write the researchers. Happiness is a different story. They cite a study showing that mood can be transmitted between people and suggest that, because people tend to mimic others to build social rapport, being around positive people forces them to mimic their happiness, thus providing more opportunities to spread happiness.

It’s a bit of a convoluted explanation, but their conclusion is pretty straightforward. Promoting friendships between adolescents, they write, “can reduce both incidence and prevalence of depression.” It’s not groundbreaking, but it underlines the need to support kids whose social networks are weaker or nonexistent.

“As a society, if we enable friendships to develop among adolescents (for example providing youth clubs) each adolescent is more likely to have enough friends with healthy mood to have a protective effect,” said Dr. Thomas House, a co-author of the paper, in a press release. “This would reduce the prevalence of depression.”