Twenge, who wrote the recent book Generations: The Real Differences between Gen Z, Millennials, Gen X, Boomers and Silents and What they Mean for America’s Future, has analyzed federally funded data conducted by the University of Michigan to examine trends in the prevalence of depressive symptoms for young adults. 

“This data set was one of the first indicators to me that we have a problem,” she tells Fortune. 

This is not sustainable pic.twitter.com/VGAOMaPG5a

— Brad Wilcox (@BradWilcoxIFS) June 21, 2023

Depressive symptoms, including feelings of “I can’t do anything right,” “My life is not useful,” and “I do not enjoy life” among 8th, 10th, and 12th graders, have been increasing for years, according to Twenge’s analysis of the data beginning in the 1990s of over 50,000 young adults. 

“This graph does definitively show that the adolescent mental health crisis did not begin with the pandemic,” she tells Fortune. “It began around 2012—a good eight years before COVID was on the scene.”  

While the pandemic brought to the forefront the unique struggles of Gen Z, it was not the sole catalyst of the increase in depressive symptoms.  

Why 2012? The data seemed misaligned with economic trends, Twenge says, but other major indicators stood out in her research. 

The year 2012 marked a time when most Americans began owning smartphones and caring about their social media presence. Meanwhile, iPhones began to monetize on the selfie with the newfound forward-facing camera, influencing the trend that has long marked the importance of appearance, Twenge adds: “Changes in technology lead to generational differences…so, things like more individualism [and] more focus on the self and less on others.” 

Social media is associated with an increase in depression and anxiety symptoms, particularly in young girls. U.S. Surgeon General Dr. Vivek Murthy has been vocal about social media’s harmful effect on teen brain development, calling for “age-appropriate health and safety standards for technology platforms” and to “require a higher standard of data privacy for children and adolescents,” according to his advisory released last month. 

“Nearly every teenager in America uses social media, and yet, we do not have enough evidence to conclude that it is sufficiently safe for them, especially at such a vulnerable stage of brain, emotional, and social development,” he wrote in a tweet announcing the advisory. “Our children have become unknowing participants in a decades-long experiment.” 

While Twenge says she cannot predict the future, the rate at which depressive symptoms have been increasing in youth is alarming. She is currently advocating for safety regulations on social media platforms, including a minimum age requirement and an age verification process. Encouraging parents to see the benefits of combating loneliness for their kids and prioritizing sleep are also ways to combat social media’s harmful effects. 

“We have to have a reckoning around teens and how they are socializing in particular,” Twenge says. “Parents need to change their thinking around teens hanging out with each other.”