On the other hand, teens who act in ways that support their Facebook friends - for example, by liking what they posted or sending them words of encouragement - decreased their levels of cortisol.
Researchers at the University of Montreal and the Institut universitaire de sante mentale de Montreal, led by Professor Sonia Lupien, found that Facebook can have positive and negative effects on teens' levels of stress hormone.
The researchers recruited 88 participants aged 12-17 years who were asked about their frequency of use of Facebook, their number of friends on the social media site, their self-promoting behaviour, and the supporting behaviour they displayed towards their friends.
Along with these four measures, the team collected cortisol samples of the participating adolescents. The samples were taken four times a day for three days. Stress levels measured in adolescents from cortisol samples are obviously not entirely due to the popular social media site, researchers said.
"While other important external factors are also responsible, we estimated that the isolated effect of Facebook on cortisol was around eight per cent," Lupien said.
"We were able to show that beyond 300 Facebook friends, adolescents showed higher cortisol levels; we can therefore imagine that those who have 1,000 or 2,000 friends on Facebook may be subjected to even greater stress," she said.
Other studies have shown that high morning cortisol levels at 13 years increase the risk of suffering from depression at 16 years by 37 per cent. While none of the adolescents suffered from depression at the time of the study, Lupien could not conclude that they were free from an increased risk of developing it.
"Some studies have shown that it may take 11 years before the onset of severe depression in children who consistently had high cortisol levels," Lupien said.
"The preliminary nature of our findings will require refined measurement of Facebook behaviours in relation to physiological functioning and we will need to undertake future studies to determine whether these effects exist in younger children and adults," she said. The study was published in the journal Psychoneuroendocrinology.