The share of college graduates with more than $40,000 in student loans grew by almost 10 times in just 8 years, a new report shows.

In 2004, just 2% of student loan borrowers with bachelor’s degrees were holding $40,000 or more in student loans. By 2012, that share jumped to 18%, according to a report released Monday by the Urban Institute, a Washington-based think tank. The bulk of bachelor’s degree recipients with student loans have relatively manageable levels of debt that they should be able to reasonably pay off, but the growing number of undergraduate borrowers taking on high levels of debt is “a reason for concern,” said Sandy Baum, a senior fellow at the Urban Institute and the co-author of the report.

The Urban Institute relied on data from the National Center for Education Statistics for the analysis.

“The thing to worry about is what kind of information people have,” Baum said. “You should be able to get a bachelor’s degree without borrowing that much money. We need to ask questions about who is accumulating more debt.”

The highest debt burdens are still reserved for graduate students, whose degrees theoretically provide them with the means to pay off their loans. But a combination of rising tuition costs, the stagnant economy, students taking longer to finish college, and the recent growth in enrollment in for-profit schools is likely contributing to higher levels of debt among undergraduates, Baum said.

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“The reason that it’s frequently wise to borrow for education is because of the payoff to it,” Baum said. “That means we should be less worried about people who borrow money who go to law school or medical school or business school.”

The borrowing patterns of undergraduates who are independent from their families are particularly troubling, the report found. These students, who are typically older, accounted for 70% of undergraduate degree borrowers who took out $50,000 or more in loans in 2012, but they made up just 56% of undergraduate degree recipients overall, the study found. Their higher levels of debt may be explained in part by the fact that they often attend for-profit colleges, where the loan balances are usually higher.

These students may also struggle more to pay their loans back because they often pursue short-term degrees, like associate’s degrees or certificate programs, that leave them with less earning power. “We have to be concerned about how older students are funding their education,” Baum said.

Policymakers and pundits should also be concerned about borrowers who don’t get their degrees at all, Baum said. While these borrowers often have relatively low debts because they attended fewer years of school, they’ll likely have trouble paying it back without a college degree.

“Students can borrow small amounts of money and really struggle,” Baum said.