2. Sociality is down

Both Steinberg and Twenge stress that the biggest problem with social media might be not social media itself, but rather the activities that it replaces.

“I tell parents all the time that if Instagram is merely displacing TV, I’m not concerned about it,” Steinberg told me. But today’s teens spend more than five hours daily on social media, and that habit seems to be displacing quite a lot of beneficial activity. The share of high-school students who got eight or more hours of sleep declined 30 percent from 2007 to 2019. Compared with their counterparts in the 2000s, today’s teens are less likely to go out with their friends, get their driver’s license, or play youth sports.

The pandemic and the closure of schools likely exacerbated teen loneliness and sadness. A 2020 survey from Harvard’s Graduate School of Education found that loneliness spiked in the first year of the pandemic for everyone, but it rose most significantly for young people. “It’s well established that what protects teens from stress is close social relationships,” Steinberg said. “When kids can’t go to school to see their friends and peers and mentors, that social isolation could lead to sadness and depression, particularly for those predisposed to feeling sad or depressed.”

This is important to say clearly: Aloneness isn’t the same as loneliness, and loneliness isn’t the same as depression. But more aloneness (including from heavy smartphone use) and more loneliness (including from school closures) might have combined to push up sadness among teenagers who need sociality to protect them from the pressures of a stressful world.