It only takes one individual in a group to begin to feel lonely for the feeling to spread to others, a US study said Tuesday.
After tracking over 5,100 people and their social contacts over 10 years, researchers found that loneliness can be contagious and that lonely, disconnected people tend to move to the fringes of social networks.
"On the periphery, people have fewer friends, yet their loneliness leads them to losing the few ties they have left," said University of Chicago psychologist John Cacioppo, the study's lead author.
Before lonely people sever relationships, they transmit loneliness to their friends who then also become lonely, according to the federally-funded study published in the December issue of the Journal of Personality and Social Psychology.
"These reinforcing effects mean that our social fabric can fray at the edges, like a yarn that comes loose at the end of a crocheted sweater," explained Cacioppo, who was joined by University of California, San Diego and Harvard Medical School researchers.
Researchers stayed in touch with the subjects every two to four years.
Using the participants' friendship histories and information about their reported loneliness, the study uncovered a pattern of loneliness showing that lonely people "infected" those around them with the negative emotion and that lonely people moved to the edges of social networks.
The next-door neighbors of lonely people who experienced an additional day of loneliness a week caused their own neighbors and close friends to feel lonely, a pattern that escalated as the neighbors shared less time together.
The study, funded by the National Institute on Aging, also found that women were more likely to "catch" loneliness from others, in line with previous work suggesting that women rely more on emotional support than men.
As with groups of monkeys, societies tend to drive away lonely members, according to Cacioppo. Research has shown that the more people are lonely, the less they trust others, which hampers their ability to form friendships.
"Society may benefit by aggressively targeting the people in the periphery to help repair their social networks and to create a protective barrier against loneliness that can keep the whole network from unraveling," said Cacioppo.