More and more states are considering feel-good legislation to tax or ban recyclable plastic shopping bags in order to promote “reusable” bags instead, but lawmakers should seriously consider the unintended consequences. Earlier this year we tested reusable nonwoven polypropylene shopping bags and found excessive levels of lead many of the reusable ones—sometimes several times what’s allowed by law.

And in a new report, University of Arizona professor Charles Gerba tested shopping carts for bacteria and found that they—and reusable bags—can be teeming with germs. Reusable bags don't inherently have bacteria, and if washed regularly probably won't. But if used often without cleaning, foods can introduce fecal coliform and other bacteria to the bags, which can take residence and grow.

On that point, previous University of Arizona research determined that 97 percent of shoppers don’t wash or bleach their reusable bags; most told researchers that they don’t worry about germs. To investigate this point further, we decided to test whether reusable bags were dirtier than a toilet seat. Watch our surprising results below:

Here's what Gerba found:

Gerba found 72 percent of the carts had a positive marker for fecal bacteria and half had Escherichia coli (E. coli). He also found reusable shopping bags that are not washed regularly are swarming with bacteria.

You read that right: Half of shopping carts tested positive for E. coli, a potentially deadly bacteria. And nearly three-quarters had germs that we typically only encounter “when nature calls.” This has profound implications for the supposedly eco-friendly push to spread the use of reusable bags. 

This bad news does make sense: Reusable bags come into contact not only with dirty shopping carts (which stores may not clean often), but also may pick up meat juices with bacteria as well. Then, fresh fruits and vegetables can come into contact with these bags.

Reusable bags are fine for those who want to (1) use them, (2) remember to pack them, and (3) consistently wash them. But if today’s report is any indication, activist attempts to force reusable bags on consumers who want a more sanitary option could backfire in a rather, well, crappy way.