Growing up in a rapidly changing and challenging world, most young people have struggled at some point or another with figuring out who they might be. Tattoos, recent research suggests, don’t just express identity: They help define it.

Although tattoos have been around for millennia, they’re more popular now than ever. In 1960, there were approximately 500 professional tattoo artists operating in the United States. By 1995, that number had risen to over 10,000. Nearly 20 years later, demand continues to surge, and by the latest estimates, roughly 20 percent of Americans have a tattoo. What’s more, 40 percent of the people in that group are Millennials, which some academics argue isn’t a coincidence.

“We’re living in this world that’s so fragmented and so chaotic,” says Anne Velliquette, a professor at the University of Arkansas who studies the relationship between consumer behavior and popular culture. Velliquette argues that we’re more able now than ever before to “recreate identities very easily,” both online and in real life.

In 1998, Velliquette and colleagues conducted an interview-based study that found people use tattoos as a way to cement aspects of their current selves. “We were hoping to look at the postmodern identity, and really what we found is that we were in this modern era where people did know who they were,” she said. “They had a sense of their core self.” Eight years later, the team revisited the idea. The second study, like the first, found that people used tattoos as a means to express their past and present selves. But the people interviewed in the second group also seemed to need proof that their identities existed at all. They relied on tattoos as a way to establish some understanding of who they actually were.

“We continue to be struck by rapid and unpredictable change,” study co-author Jeff Murray said at the time. “The result is a loss of personal anchors needed for identity. We found that tattoos provide this anchor. Their popularity reflects a need for stability, predictability, permanence.”

For people who study identity, this permanence is key. We define who we are by the elements that stick with us—people, stories, places, memories—and we measure ourselves in relation to them, patching the highlights together into what sociologists call a “personal myth.” These myths make sense of often-turbulent lives, integrating our “remembered past, perceived present, and anticipated future,” as Velliquette wrote in her 2006 report. Some people use institutions such as religion, work, and family to create this myth. Others use material objects like houses and cars to define it. But Millennials are something of a breed apart. Without access to many of the anchors their parents had to create their personal myths, that sense of stability and permanence is often harder to find.