Did you spend some time on Facebook today? If so, it probably made you just a little bit sadder. That’s the troubling conclusion of a study of Facebook use and well-being, published today in PLOS ONE. The result is counterintuitive, because abundant psychological research finds that contact with friends and family is crucial for well-being. So it would seem that Facebook should be an ever-flowing fountain of happiness. If you’re stuck at a desk job all day or even completely isolated, as long as you have Facebook, you have “friends.” Why else would half of the world’s 1 billion Facebook users log in every day? But are those cold, glowing pixels a good substitute for real-world contact? Surveys of Facebook users find mixed results. The problem is that standard polls of people at a single point in time can’t distinguish whether any unhappiness associated with Facebook use is due to biased sampling—for example, if people use Facebook more often when they’re already unhappy. The new study cut through that problem by text-messaging people five times a day for two full weeks. Each message contained a link to an online survey that asked participants about their contact with other people, Facebook use, and general well-being and satisfaction. Not only did Facebook use predict a drop in happiness—people tended to be sadder by the end of every visit to the Facebook site—it also predicted a drop in people’s satisfaction with life slightly over the course of the study. That prediction held up even after controlling for differences in the frequency of real-world contact, the size of people’s Facebook networks, degree of loneliness, and self-esteem. What a bummer.