“Consumers — Gen Zs, especially — are sick of being told by these huge companies that they need to look a certain way, that they need to buy so-and-so products to fix their flaws,” Ms. Collins said. “They’re rejecting traditional forms of advertising that don’t do anything but tear down your confidence.”

Yet a movement that points to social media as a culprit is also using the same platforms to get its message across.

“There’s a cultural shift happening where people are becoming more honest,” said Matt Traube, a psychotherapist in San Luis Obispo, Calif., who specializes in skin conditions. “Tampering with photos on social media has become such a phenomenon that people are beginning to see how destructive it is. At the same time, social media gives us the opportunity to create these powerful social movements.”