But she said the need for social approval and support is universal.

“We all have levels of insecurity,” Dr. Fox said. “When someone is like, ‘Here is my cancer selfie,’ you are feeling vulnerable right now. You need that social support. That is not saying you are a narcissist for putting it out on social media.”

After all, people have been making self-portraits for centuries, in remarkably similar ways. The 16th-century artist Parmigianino famously painted a portrait of himself with his arm extended. A self-portrait by Rembrandt van Rijn, a 17th-century Dutch artist, shows an expression similar to the classic “duckface” selfie. And during the Italian renaissance, at least one artist used a self-portrait for “calling cards,” as a way to market their work.

Since the term “selfie” first caught on — it was the Oxford Dictionaries’ word of the year in 2013 — researchers have identified three types of selfie-takers.

There are communicators, who want to have a two-way conversation (for example, a post with an “I Voted” sticker to encourage civic engagement); autobiographers, who document their lives for their own purposes, rather than seeking feedback or compliments (a selfie at home with a favorite coffee mug, or a photo at the Grand Canyon); and self-publicists, who want to build a brand and positively curate an image (à la the Kardashians).

“They have become so common that my grandma does them when we get together,” said Steven Holiday, an author of the study who argued that the notion of the selfie as narcissistic is outdated.

“We have gone beyond the self-centered nature — we need to let it go when it comes to selfies,” he said. “Selfies are a way for us to connect and communicate, and feel more personal with people all around the world.”