After a summer full of travel, I know I'm home in San Francisco when I see all the reusable bags at the checkout line at my Whole Foods Market. To a San Franciscan, forgetting your reusable bag when shopping for groceries is almost as irresponsible as forgetting your wallet. What will you carry your food in, if not a green bag? San Francisco banned hard-to-recycle plastic bags in grocery stores more than three years ago. Whole Foods Market was on the forefront of this initiative; we discontinued the use of plastic bags at checkout in stores across the country. While paper bags are still an option for customers, it's now commonplace for customers to BYOB (bring your own bag). Using a re-usable bag translates into less energy used, less solid waste produced and fewer waterborne wastes. While these environmental benefits clearly support the use of re-usable bags, nothing is ever foolproof. I recently heard a report about bacteria growing in these beloved reusable bags. The report, I discovered, was published by the Environment and Plastics Industry Council. While there is some inherent bias there, the report did have some good suggestions. The study took a sampling of the bacteria content in bags used more than once and concluded that "the bag surface can harbor or breed substantial bacterial populations. Bacteria may be growing in your re-usable bag if it isn't washed properly. The moist, dark, warm interior of a folded reusable bag that has acquired a small amount of water and a trace of food contamination is an ideal incubator for bacteria. Close to 30 percent of bags tested had elevated levels of bacteria, and several tested positive for mold or yeast." Wait! Don't go back to plastic quite yet. It's important to remember that bacteria is everywhere in our environment, but it's not the end of the world. No harmful strains of E. coli or Salmonella were detected in any of the bags tested in this study and in fact, no outbreaks of disease have been linked to reusable bags. However, this study is a reminder that as a precaution, you should wash your bags to prevent bacteria overgrowth and subsequent food contamination. After learning that my bags might be an "incubator for bacteria," I threw them in the wash and hung them to dry in the sun. While I was at it, I went through my collection of reusable bags and tossed a few into the recycling bin that were looking a little old and grungy. Like most San Franciscans, I have bags in my car, in my closet, in my storage unit…it's a little out of control. When you think about the potential to pick up some unwanted bacteria during a shopping excursion based on all the things you touch (the bus on the way to the store, the bathroom door, the checkout counter), the probability that your bags are carrying around some bacteria as well makes sense. The nagging from our mothers to "wash your hands!" needs to be reinforced from time to time and should be extended to our bags as well. So, like mom said, Wash your hands! And while you're at it, wash your bag with equal care to eliminate the potential for cross-contamination. The possibility of transmitting germs by using a reusable bag can be eliminated with a little good housekeeping. Here in San Francisco, we have a reputation to uphold as green mission trendsetters! We can't let a fear of germs slow down our momentum to save the planet, one reusable bag at a time.