The latest data from the U.K.’s Office for National Statistics (ONS) shows that 9.25 million working-age adults weren’t looking for a job, also known as being economically inactive, in the last quarter of 2023. 

It’s a troubling rise in inactivity that has been supercharged by young people, with three million working-age adults under 25 now registering as not looking for work.

While many of these people are students, statisticians have signaled the increase in youth worklessness as particularly alarming.

Young people quitting the workforce

“An important trend that we are seeing there is young people. If we look over the last year we’ve seen that increases in inactivity have been concentrated in the younger age groups, particularly in that 16 to 24-year-old age group,” Liz McKeown, director of economic statistics at the ONS, told BBC Radio 4.

By the end of last year, 4.5% of 16-24-year-olds were not actively looking for work. That compares with just 0.1% of young people registering as inactive in the first quarter of 2020.

This comes despite ONS data suggesting there were 908,000 vacancies in the last quarter of 2023. Although the number has fallen for the last couple of years, it remains above pre-COVID levels.

It’s the latest concerning data point to signal growing workplace detachment from young people that continues to confound policymakers. 

There is growing worry that the rise in worklessness isn’t an economic phenomenon, but one revolving around deteriorating mental health among young people.

“Worryingly, these soaring levels of inactivity have coincided with a youth mental health crisis,” said Louise Murphy, a senior economist at the U.K.’s Resolution Foundation (RF) think tank.

“18-24-year-olds are now more likely to experience a common mental disorder than any other age group – and it is lower-qualified young people who are facing the worst economic consequences, with non-graduates with mental health problems significantly more likely to be workless than their graduate peers.”

Murphy told Fortune that changes were needed in the workforce and in the educational system to ensure young people were given adequate mental health support before starting careers.

Mental health crisis carries into the workplace

Gen Zers and younger millennials are exhibiting several signs of struggling to adapt to the workforce. 

While this has historically been a cross-generational issue, there are signs that it’s taking a particularly large toll on the newest crop of young workers.

For those young people who have managed to make it into the labor market, a rising tide of data suggests the struggles with mental health don’t end once they receive a job offer.

Research from the RF found that Gen Z workers were taking more sick leave than Gen Xers 20 years their senior, marking a symbolic turnaround in historic absence trends. 

The think tank blamed rising sickness on a mental health crisis among young people, pointing out that more than a third of 18-24-year-olds suffered from a “common mental disorder” (CMD) like stress, anxiety, or depression. 

“Youth worklessness due to ill health is a real and growing trend; it is worrying that young people in their early 20s, just embarking on their adult life, are more likely to be out of work due to ill health than those in their early 40s,” RF researchers said. 

A collective rise in inactivity is also having an effect at the aggregate level of the U.K. economy. 

The ONS observed that the typical U.K. worker had dropped their working week by 0.3 hours between 2019 and 2022. This fall was driven by men, who were working almost an hour per week less than they were in 2019. 

The statistics body said this was beginning to have an effect on economic growth, particularly since the onset of the COVID-19 pandemic.