A new study from Arizona University and Loma Linda University shows the bags can be a Petri dish for germs and bacteria.
Researchers randomly tested shoppers' reusable bags as they walked into groceries stores. They say E. coli and other bacteria were found in many of the eco-friendly bags .
Ninety-seven-percent of the people interviewed said they had never washed or cleaned their bags.
On top of regular cleanings, researchers say it's important to separate raw foods and meats from other products.
The study was funded by the American Chemistry Council.