Don't press the like button: Facebook is a bummer that makes us feel worse about our lives, according to new research. Facebook users in a study led by the University of Michigan wound up feeling worse about themselves after two weeks, and their mood darkened the more they browsed the social medium. It didn't seem to matter how big their network was, how supportive they thought their friends were, nor why they went to Facebook in the first place, according to the study, published online in PLoS One. "We were able to show on a moment-to-moment basis how people's mood fluctuated depending on their Facebook usage," said University of Michigan social psychologist Ethan Kross, lead author of the study. "We measured lots and lots of other personality and behavioural dimensions, like, for example, frequency of Facebook use. But none of the factors that we assessed influenced the results. The more you used Facebook, the more your mood dropped." The study adds to a body of work examining social media's effect on well-being, much of it offering mixed diagnoses. Looking at your own profile can be self-affirming, according to a recent study. And a survey of Facebook users suggested it modestly increased life satisfaction, social trust and civic engagement. But none of those studies followed people over time. The University of Michigan study involved 82 college-aged volunteers - a core demographic among Facebook's 700 million active daily users - who answered questionnaires five times a day for 14 days, and rated their well-being at the beginning and end. Worry did not predict changes in Facebook use, but loneliness did, according to the study. Nonetheless, when researchers controlled for loneliness, the relationship between Facebook use and mood and satisfaction were insignificant. "Loneliness predicted Facebook use, and loneliness also predicted how bad people felt," Kross said. "But the effect of Facebook on how people felt was independent of loneliness. "One of the things we don't know is what aspect of Facebook use is contributing to these results," he said. "Facebook and online social networks more generally represent a very new way in which human beings are interacting, and we're just beginning to scratch the surface as to how exactly these interactions work and how they influence us." Catalina Toma, a University of Wisconsin communication researcher who found that Facebook users could increase their self-esteem, said seemingly contradictory findings reflected the complexity of the medium and pointed out the need to drill deeper into what people do while on Facebook. "Facebook is such a gigantic space where so many different activities take place," said Toma. "So for us to be simply talking about Facebook use is an oversimplification. Facebook use is not just one thing; it is many, many different things."