You know about the horrors of plastic grocery bags: They pollute the environment, maim and kill wildlife and languish in landfills. It’s estimated it will take up to 1,000 years for a plastic bag to decompose.

There's no question reusable bags are the way to go. But while your earth-friendly totes are helping to save the environment, they may be affecting your health in surprising ways. 

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Does your bag influence what you buy? 

Shopping with reusable bags may affect what you put into them, according to a study published in the Journal of Marketing. It found that folks who use them buy more organic produce — and also more junk food. “They may feel they have license to do so after the virtuous act of bringing their own bags to the store,” says Bryan Bollinger, PhD, assistant professor of marketing at Duke’s Fuqua School of Business and the study’s co-author.

If you notice you’re bringing home more junk food than you want to when you use reusable grocery bags, try not to shop on an empty stomach. And steer your cart away from the inner aisles of the supermarket, where most processed foods are shelved.

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Bacteria: It's in the bag

Last week’s groceries can leave behind germs that might infect this week’s haul. Although there’s an easy way to avoid this — wash bags often, after every use, if possible — few people do. “According to a recent survey conducted by the Academy of Nutrition and Dietetics and ConAgra Foods, only 15 percent of Americans wash their reusable bags,” says Libby Mills, MS, RDN, a spokesperson for the Academy of Nutrition and Dietetics.

According to the American Cleaning Institute, most polypropylene and natural fiber bags can be laundered and dried in the dryer. Nylon and polyester bags, including insulated ones, should be washed by hand and allowed to air dry. Once bags are clearly worn or torn, it’s time to replace them with new ones.

An easy way to prevent foods that won't be cooked from becoming contaminated with bacteria such as salmonella and E. coli is to designate specific bags for specific food categories. “Cross-contamination can occur when juices from raw meat come in contact with cooked or ready-to-eat foods,” explains Mills. You can designate bags by color (red for raw meats, green for fresh produce, blue for prepared food, for example). Or, if you’d rather not use bags that are dyed, label plain bags with a fabric marker. 

Other ways to prevent germs from flourishing: 

  • Use grocery bags for groceries only. Don’t let your kid grab one to carry baseball cleats in or to tote books back to the library. “Microbes from meat or fish that are left behind can leak onto other items. The reverse is true as well — germs from the soles of shoes and sweaty clothes can come in contact with food,” says Mills. 
  • Don’t store bags with the junk in your trunk. The Department of Agriculture recommends keeping reusable shopping bags in a cool, dry place in the garage or house, rather than in the trunk of the car, where heat and humidity can allow germs to flourish. It’s fine to keep your (freshly washed) reusable bags in your car, though, as long as they don’t come in contact with dirty surfaces. Stash them in one big bag or in the glove compartment, suggests Mills.
  • Keep cold things cold. Insulated bags (also reusable) won’t buy you a lot of time in terms of keeping foods out of the danger zone (between 40 degrees F and 140 degrees F). Even so, they’re a good safety precaution. “There might be an unpredictable or incidental circumstance like a flat tire or phone call that prevents you from going straight home to load cold items home to the refrigerator or freezer,” explains Mills.

Lead in bright bags?

Some reusable bags are plastic, either woven or non-woven polypropylene (often created from recycled containers). Others are nylon or polyester (a petroleum product). You also can find bags made from natural fabrics such as cotton, bamboo or hemp. While the material doesn’t matter so much, you should pay attention to the color of bags. “There’ve been reports of lead in some brightly colored bags, particularly in paint used for logos and lettering, so stick to plain, color-free bags if you can,” advises Mills.

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Jennifer Kelly Geddes is a New York City-based writer and editor who specializes in parenting, health and child development. She’s also the mom of two teen girls.