About one in five U.S. households now carry some form of student loan debt -- the highest share ever, according to a new Pew Research Center study.

The number of households with student debt is now 19 percent, more than double what it was 20 years ago. The numbers are worse for young people, with 40 percent of households headed by someone under 35 owing on student loans. The reasons for an increased share of households taking on student debt can be chalked up to a number of factors.

First, more students are pursuing higher education than ever before. Between 2000 and 2010, enrollment in higher education increased 37 percent.

Secondly, higher education is getting more and more expensive while federal subsidies for poor students are remaining generally stagnant. The Pell grant, given to low-income students to pay for college, paid for about 40 percent of the total cost of college in 2001-02. As recently as 2005, they were estimated to cover only about a quarter of all college expenses. With tuition increasing at a rate that far outpaces inflation, federal financial aid simply cannot keep up.

The average amount owed on student loans in 2010 was $26,682 (though the median is less than half that amount), and though most students don't carry high debt levels, the percentage of people carrying extremely high student loan balances is on the rise. "In 2007, 10% of student debtors owed more than $54,238," the Pew study said. "By 2010, 10% of student debtor households owed more than $61,894 (all dollar figures adjusted for inflation and in 2011 dollars)."

Generally, students who end up with high debt loads end up taking it on due to high-priced graduate programs, but it's now no longer uncommon for students to emerge from a four-year program with more than $30,000 in student loan debt.

"Because outstanding student debt has been rising and household incomes have been falling since 2007, outstanding educational debt has risen as a share of household income for all income groups considered," the Pew study said.

The good news the majority of students seeking higher education don't have to borrow. A Sallie Mae survey released last month found that 65 percent of students don't borrow to pay for higher education.

[Student loan piggy bank via Shutterstock]