London: In today's hurly-burly world, logging on to social networking websites may be the most popular way to know about each others' lives, but it can also make you sad, as per the researchers.

A new study, led by sociologists Hui-Tzu Grace Chou and Nicholas Edge, at Utah Valley University has found the more hours people spend on social networking sites, like Facebook, the stronger is their belief that others are happier.

The researchers claim that the carefully chosen pictures of cheerful faces which Facebook users tend to upload on their pages actually portray a debilitating message to others.

"Looking at happy pictures of others on Facebook gives people an impression that others are 'always' happy and having good lives. While Facebook users will know that their real friends have ups and downs in their lives, all they have to go on with their fake Facebook 'friends' is a smiling picture," Chou said.

For their study, the researchers interviewed 425 undergraduate students about their happiness and that of their friends. The subjects were asked how much they agreed or disagreed with statements such as "Life is fair" and "Many of my friends have a better life than me".

The students then described their Facebook activity including their number of "friends". Some 95 percent used the website and on average they had been there for two-and-a-half years, and spent nearly five hours a week on it.

The findings, published in the 'Cyberpsychology, Behaviour and Social Networking' journal, revealed that "the more hours’ people spent on Facebook, the stronger was their agreement that others were happier".

Conversely, the study found that people who spent more time actually socialising with friends in person were less likely to feel they had been handed life's short straw.

"This Facebook-related dissatisfaction is the result of a common psychological process known as 'correspondence bias' in which we draw false conclusions about people based on limited knowledge," Chou said.