In an eye-opening piece in The Atlantic, Jean M. Twenge, PhD, doesn’t mince words about how technology has transformed today’s teens: “The arrival of the smartphone has radically changed every aspect of teenagers’ lives, from the nature of their social interactions to their mental health,” she writes.

Twenge, a professor of psychology at San Diego State University, has been researching generational differences for 25 years. Her Atlantic piece provides a nuanced and data-filled perspective on how iGen (Twenge’s term for people born between 1995 and 2012) have been impacted by tech—and it’s not good. “It’s not an exaggeration to describe iGen as being on the brink of the worst mental-health crisis in decades,” Twenge writes. Twenge wrote the forthcoming book iGen: Why Today’s Super-Connected Kids Are Growing Up Less Rebellious, More Tolerant, Less Happy — and Completely Unprepared for Adulthood — and What That Means for the Rest of Us, which traces many of the problems iGen faces back to 2012, the “moment when the proportion of Americans who owned a smartphone surpassed 50 percent” she writes.

The title of her book perfectly sums up her Atlantic piecethough it’s worth reading in its entirety. While teens are physically safer than they’ve ever been (for example, with access to the world at their fingertips, they don’t leave the house much as past generations did), they’re missing out on normal teen experiences like rebellion and a desire for autonomy. But more importantly, their health is on the line: teens today are at increased risk for everything from social isolation and increased rates of suicide to impaired sleep, as Twenge writes. Sleep especially, so essential to teens’ overall well-being, is being compromised by technology: using smartphones at night (or sleeping with them, as many teens told Twenge they do) can lead to sleep deprivation, which in turn can impair mood and reasoning and make you more susceptible to a host of both short and long-term physical problems.

Twenge also explores how teens today stack up to generations past and what that means for the future of iGen. Read the full piece here