Japan had more than four million middle-aged “parasite singles” who lived with their elderly parents in 2016, according to new research data.

That’s around 4.5 million unmarried citizens aged 35 to 54 who were either unemployed or underemployed, the country’s Statistical Research and Training Institute found.

The situation poses difficulties for Japan, which currently struggles with an aging population and declining birth rates. Altogether, such problems make up what experts are calling a “demographic time bomb.”

Today’s situation of Japan’s parasite singles goes back to the 90s, when they, at the time, were carefree 20-year-olds who believed that they’ll have no problem marrying in their 30s. But as the times turned out, a significant number failed to wed and are now at the brink of becoming elders themselves.

Masahiro Yamada, the sociologist who coined the phrase “parasite singles” in 1997, told Reuters:

“During the ‘bubble economy’ until the mid-1990s, the 20-somethings were happily amusing themselves. They thought by the time they were in their 30s, they’d be married. But one-third never married and are now around age 50.”

Parasite singles are facing ginormous challenges, the most obvious of which is financing as they continue to rely on their elderly parents who may not be with them for much longer. Because they have no pensions or savings, they would add up to the burden of a social welfare system that’s already struggling partly due to a shrinking workforce, the Japan Times wrote.

Among them is Hiromi Tanaka, 54, who relies on her mother’s pension while holding private singing lessons. But with a dwindling number of students, her future looks nothing short of miserable.

“I got used to living in an unstable situation and figured somehow it would work out,” she told Reuters. “My father died last year so pension income was halved. If things go on like this, my mother and I will fall together.”

While one could argue that parasite singles had every opportunity to make their lives better, many from the pack assert that they did not choose their current lifestyle. Instead, they claim that the economy is responsible.

Experts say that the rise in low-paying, unstable jobs partly affected those who chose not to get married. Other parasite singles were once employed but were laid off after corporate restructuring and personal reasons such as illness.

Despite some decline in the numbers of singles depending on their parents, economist Katsuhiko Fujimori forecasts that the parasitic trend would most likely persist. He explained why:

“That’s because of the increase in irregular workers and the fact that more and more people cannot marry for economic reasons, even if they want to.”