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They’re called hikikomori: the 541,000 people across Japan between ages 15 and 39 who live as shut-ins. The Japanese government defines them as people who have stayed at home for at least six months and haven’t had any social interactions beyond their family, Maiko Takahashi reports for Bloomberg.

Linguistically, the word a combination of the hiku, or “draw, pull” and komoru, or “seclude oneself.” The standard definition is “acute social withdrawal.” The phenomenon was first identified in 1978 as “withdrawal neurosis,” then further described by Japanese psychiatrists in the 1990s, before turning into a subject of national and international interest in the 2000s, being added to the Oxford English Dictionary as a loanword in 2010.

Now, Takahashi reports, Prime Minister Shinzo Abe wants to mobilize the nation’s shut-ins to contribute the world’s third-largest economy as it faces a massive population drop. From a health perspective, that kind of self-enforced solitude is brutal: American researchers have found that loneliness poses an increase of risk in mortality comparable to obesity.

A 2015 review proposed three possible reasons someone might turn hikki. It could be that “overdependent” youths grew up in smothering families where they never gained autonomy or learned to trust people; “maladaptive interdependent” youths grew up in dysfunctional families, leading to bullying and unsatisfying relationships at school; and “counterdependent” youths are so burdened by high academic and career expectations that they withdraw.

The prevalence of hikikomori also speaks to the culture of mental health in Japan. A 2010 Journal of Nervous and Mental Disease paper proposed that hikikomori is used by laypeople to describe other mood disorders that they may not be familiar with, and that mental-health professionals may use it as a gentler way to talk about other issues, since clinical depression and its ilk are so highly loaded. The researchers reference a 2008 study of 97 clinical hikikomori patients which found that 26 percent had anxiety disorders, 8 percent had schizophrenia, and 23 percent had some sort of personality disorder — indicating that what manifests as hikikomori may be the result of one or more underlying, and possibly underdiagnosed, conditions. A 2011 pilot study found that similar sorts of social withdrawal exist around the world; surprisingly, some Japanese clinicians thought it didn’t demand intervention, while other countries recommended hospitalization.

Princeton cultural anthropologist Amy Borovoy has argued that the reason Japan has comparatively low self-reported mental illness isn’t an indication of society-wide mental health, but heavy stigma. “Doctors, aware of the sensitivity of the families, avoid diagnosing major psychopathology to the extent that it is possible,” she wrote in a 2008 paper. If Abe wants to bring the hikikomori back into society, it might require changing that culture, too.