How Worried Should I Be About Bacteria on Kitchen Sponges?

I live in NYC with my husband and two kids under 5, and we don’t have a dishwasher — we are the dishwashers. I’ve read a few things over the years about how dish sponges generate a whole lot of bacteria (precise enough calculation for a data expert?), but I’m not sure what to do about it. How much does daily sponge usage affect our health, whether by ingesting bacteria or the materials that sponges are made of? Does microwaving sponges actually do enough to reduce the “bad stuff,” or should we just ditch the sponges altogether and use something else (e.g. those mesh things that my mom loves to tout as the answer to the bacteria problem)?

—Deep in Dishes

This is a question I love. Not only because one of my most long-standing spousal disagreements (dating back to 2002) is about sponges in the sink, but also because it was an opportunity to dive deep into the world of academic food-contamination science.

The first thing I learned is that if you look for academic papers on “sponge bacteria,” you get a huge set, but … they are about bacteria that live symbiotically with sea sponges. So interesting! Not relevant to this question.

Fortunately, there is also a large literature on kitchen sponge bacteria. As you recognize, kitchen sponges harbor bacteria — salmonella, E. coli, etc. This isn’t surprising. Wet, warm conditions with food residue are basically a bacteria’s dream home. Let’s posit, then, that your sponges are chock full of exciting bacteria. The two important follow-up questions: does it matter, and how could you prevent this?

On the question of whether it matters, you want to think about where the bacteria ends up. You are not sucking on the sponge directly. The concern is that the sponge would transfer bacteria to plates or surfaces and then onto food. At least one helpful paper has tried to quantify this, and, reassuringly, it finds that while bacteria definitely transmit to clean plates, they do not seem to transfer well to most food. So — that’s good!

There is a nuance here: we’re all exposed to some bacteria all the time, and it usually doesn’t make us sick. If you’re immunocompromised or have an infant in the house, you do want to be a little more careful about bacterial exposure, and it may make sense to think about how to avoid spreading the sponge bacteria onto everything else.

On the question of how to limit bacteria, the literature also has much to say. First, antibacterial dishwashing liquid appears to be a waste. What works very well for disinfecting sponges is running them through the dishwasher (see, e.g., here). This is maybe less helpful for you, since the reason you’re using the sponges is you do not have a dishwasher, but it may be helpful to others. The microwave results are mixed, but at least some studies do suggest you can microwave the sponge for a minute and that will limit bacteria. Boiling can also work, although that’s quite a lot of effort.

Bottom line: Yes, there’s bacteria, but probably if you’re all healthy, you should just not worry about it. It wouldn’t kill you to run it through the microwave occasionally. Oh, and the logic is pretty clear that bacteria will grow on anything, so I would not bother with your mother’s advice.