Social media sites designed to help people connect are actually causing them to feel more alone, say psychologists.
The more time young adults spend on platforms such as Facebook, Twitter and Pintrest, the more likely they are to feel cut off from the rest of society, a study has found.
More than two hours of social media use a day doubled the chances of a person experiencing social isolation.
Higher numbers of visits to social media sites have a negative effect as well as the amount of time spent online, the US research shows.
Study participants who visited various sites 58 or more times per week were three times more at risk of isolation than those visiting less than nine times per week.
Lead scientist Professor Brian Primack, from the University of Pittsburgh School of Medicine, said: "This is an important issue to study because mental health problems and social isolation are at epidemic levels among young adults. We are inherently social creatures, but modern life tends to compartmentalise us instead of bringing us together.
"While it may seem that social media presents opportunities to fill that social void, I think this study suggests that it may not be the solution people were hoping for."
The team questioned 1,787 adults aged 19 to 32 about their use of the 11 most popular social media platforms at the time the research was conducted in 2014: Facebook, YouTube, Twitter, Google Plus, Instagram, Snapchat, Reddit, Tumblr, Pintrest, Vine and LinkedIn.
Each person was assessed for self-perceived social isolation using a standard technique called the Patient-Reported Outcomes Measurement Information System (Promis) that provides scores for a wide range of measurements.
The link with isolation was found even after taking account of social and demographic factors that might have influenced the results.
Co-author Elizabeth Miller, professor of paediatrics at the University of Pittsburgh, said: "Even if the social isolation came first, it did not seem to be alleviated by spending time online, even in purportedly social situations."