You’re lonely and ill at ease. A friend says something you feel is mean-spirited and you tell her she’s being unkind. Next time you talk, it’s awkward. Gradually, you drift apart.

Without knowing it, you’ve transmitted loneliness — a sense of social disconnection. But it doesn’t stop there: Your friend is more likely to convey this uncomfortable feeling to someone else, who in turn may spread it to yet another person.

So it goes in social networks, according to new research by John Cacioppo, director of the Center for Cognitive and Social Neuroscience at the University of Chicago. Unwittingly, we pass feelings to others — whether in person, on the phone or online — and influence the pattern of human connections surrounding us.

Previous studies have found that obesity, smoking and happiness can spread from person to person. Cacioppo’s research, published Tuesday in the Journal of Personality and Social Psychology, shows that loneliness also has this social dimension.

Analyzing decades of data from the Framingham Heart Study, he found that individuals who feel isolated are more likely to lose friends over time. Women pick up a feeling of loneliness more readily from friends than do men.

Ultimately, loneliness is a biological signal like hunger or thirst, Cacioppo argues. It tells people they’re not sufficiently connected and that they need to re-establish human bonds. At the same time, it’s an emotional irritant that can make us uncomfortable and hard to reach. Often, friends just stop trying.

This holiday season there will be many lonely people among us. To them, we can be kind. “Expect the best of people,” Cacioppo says, noting that we get what we give in human relationships.

Loneliness as a virus or disease? Interesting research. Keep a close eye on this one.