Some diseases are contagious–like colds, flu, and chicken pox. But what about loneliness? Loneliness may not be a disease, at least not in the same way that chicken pox is. But loneliness can be contagious.

How so? The same way that many emotions can be infectious. Being around someone who’s really happy can put you in a good mood. While hanging around someone who’s depressed can be, well, depressing.

The same goes for loneliness. According to one study, the average person feels lonely about forty-eight days per year. Having a lonely friend adds around seventeen extra days of lonely feelings.

Following more than five-thousand people for ten years, the study observed how loneliness can spread through a group. Lonely people, it seems, transmit their sad, lonely feelings to people around them. What happens, according to the study, is that interacting with a lonely person can leave you with a negative feeling toward friendship generally.

And so you’re more likely to have negative experiences with other friends, weakening social bonds. If loneliness is allowed to spread unchecked, it can destroy a social network.

The best way to ward off this sort of lonely contagion is to pay more attention to people on the edges of a group. Reaching out to those who are shy or don’t fit in, and are therefore lonely, can make them feel less alone. And so they’re less likely to spread lonely feelings throughout the group.