Taking an Instagram selfie doesn’t make you a narcissist – but it might just turn you into one. That's according to a study recently published in The Open Psychology Journal.

Researchers at Swansea University, UK, and Milan University, Italy, found that people who regularly check into social media accounts on Instagram, Facebook, Twitter, and Snapchat to post selfies exhibited an increase in narcissistic behavior over a four-month period. And it wasn't just a modest increase – narcissistic behavior rose by an average of 25 percent.

"There have been suggestions of links between narcissism and the use of visual postings on social media, such as Facebook, but, until this study, it was not known if narcissists use this form of social media more, or whether using such platforms is associated with the subsequent growth in narcissism," Phil Reed, a professor of psychology at Swansea University, said in a statement.

"The results of this study suggest that both occur, but show that posting selfies can increase narcissism."

To find out exactly how much influence social media exerts over our behavior, the team monitored social media use and changes to personality using the Narcissism Personality Inventory and Problematic Internet Use Questionnaire each side of a four-month window. In total, 74 people aged between 18 and 34 were involved who, between them, averaged three hours on social media per day excluding any use required for work. Only one abstained from social media altogether and some reported using social media for up to eight hours a day.

Overall, Facebook was the most popular platform, used by 60 percent of the participants. Instagram lagged behind at 25 percent, followed by Twitter and Snapchat (both 13 percent). More than two-thirds of the group reported using social media primarily as a way to upload and share images. 

The results suggest that people who frequently posted images displayed a 25 percent rise, on average, in narcissistic behavior, such as grandiose exhibitionism, feelings of entitlement, and the exploitation of others. What's more, this increase took several participants over the clinical cut-off for Narcissistic Personality Disorder.

"Taking our sample as representative of the population, which there is no reason to doubt, this means that about 20% of people may be at risk of developing such narcissistic traits associated with their excessive visual social media use,” Reed added.

Because the results showed a time lag between what the researchers categorized as "problematic Internet use" at baseline and an increase of narcissism four months later, it suggests that the first triggers the latter – even if the study design is correlational rather than causational. Interestingly, the same relationship was not observed for those whose primary use for social media was verbal rather than visual. However, levels of narcissism at baseline did predict an increase in this verbal media use four months down the road, suggesting the reverse relationship. 

The study was limited to 74 subjects so should be met with some caution. And while it reflects the stereotype of the narcissistic selfie-poster, it doesn't explain why that might be – though Professor Roberto Truzoli from Milan University has put forward his theory.

"The use of visual social media may emphasize the perception of narcissistic individuals that they are the main focus of attention," he said.

"The lack of immediate 'direct' social censure, may offer them the opportunity to inflict aspects of their narcissistic personality, present themselves in a grandiose manner, and realize fantasies of omnipotence."

So there you go, just one more reason to log out of social media.