Q: I’ve heard that you don’t have to wash breast-pump parts between sessions because breast milk kills germs. Is that true? I pump at work and not having to wash and rinse breast-pump bottles and shields during the day would save me a ton of time, not to mention potentially embarrassing run-ins in the office bathroom.

A: What you’ve heard is partly true: Human milk is naturally anti-bacterial. “Human milk is very effective at killing bacteria for about 12 hours after it leaves the breast,” says Mary Rose Tully, director of Lactation Services at North Carolina Women and Children’s Hospitals in Chapel Hill, NC.

“But we don’t know what the effect is if it starts drying or is exposed to large amounts of pathogens,” she says. So you should wash breast-pump bottles and shields between sessions.

But if you don’t have time, place them unwashed in a clean plastic bag, such as a Ziploc, and store them in the refrigerator, Tully advises. But be sure to wash them thoroughly at least once a day when you get home.

See our reports on breast pumps, best breast pumps for working mothers, and safety tips for breastfeeding for more information.