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PHILADELPHIA (CBS) — Frequently posting selfies on social media has been proven to increase narcissism in people, a new study finds.

Researchers from Swansea University and Milan University monitored 74 adults between ages 18 and 34, measuring their level of narcissism using tests commonly used to diagnose Narcissistic Personality Disorder.

Participants — and their social media accounts — were tracked for four months to see if any personality changes occurred.

“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,” study leader Phil Reed, a psychology professor at Swansea University, said. “The results of this study suggest that both occur, but show that posting selfies can increase narcissism.”

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The study found that participants who used social media frequently, particularly those who posted selfies, showed a 25 percent increase in narcissistic traits, with some even qualifying for Narcissistic Personality Disorder.

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

At the same time, those who were still on social media frequently, but sent tweets or posted text, exhibited no such increase in narcissistic traits.