The survey of 1,000 people, conducted by Opinion Research Corp. for the Guardian Life Insurance Co., found 23 percent of U.S. adults say they have zero savings to cover medical expenses, while 10 percent have less than $1,000 saved.

One-third of those using credit cards to pay for critical illness expenses charge more than $5,000; 1 in 7 charged more than $25,000, the survey says.

Of those respondents who do not have savings, 40 percent say they would turn to family to pay bills related to critical illness; 23 percent would seek a second mortgage; 18 percent would use credit cards; and 14 percent would ask friends for the money.

Seventy percent of employees believe they would suffer financial stress if they had to cope with a critical illness, while 30 percent say their family would suffer financial hardship if this occurred.

The survey has a margin if error of plus/minus 3.1 percentage points.