Colon cancer is on the rise among young Americans, according to new findings from the Center for Colon Cancer Research at the University of Southern California, and researchers aren’t sure what’s causing the alarming trend, FOX WACH reports.

Typically, colon cancer affects people over age 50, which is why screenings via colonoscopy are not generally recommended before then. But according to USC researchers, the rate of colorectal cancers in people younger than 50 has nearly doubled over the past few decades; indeed, people in their 20s are being diagnosed with the illness.

Some scientists wonder whether the rise in colon cancer among young people is the result of not getting screened or whether diet and lifestyle are to blame. Others are researching family histories.

Franklin Berger, MD, director for the Center for Colon Cancer Research Department at USC, told FOX WACH that tumors tend to be located closer to the rectum in younger people whereas they are more spread out in older folks and that there appear to be very different underlying genetic components to colon cancer between the two age groups. What’s more, younger people aren’t as likely to have the kind of risk factors for the illness that older adults do, such as obesity or poor diet. Those who lead healthy lifestyles and have good eating habits can still be vulnerable.

Because of insurance rules and lack of funding, it’s difficult to authorize testing for colon cancer for those under 50 (those with a family history can be authorized to be screened at 45). Cancer researchers, therefore, are working to develop more cost-efficient ways to screen for colon cancer in young people, including through urinary and/or stool samples.

Meanwhile, colon cancer is currently the fourth most common cancer in the United States, and the second-leading cause of cancer deaths. Anyone over age 50 should be screened regularly.