Science & Technology

Kitchen Sponges Are Even Grosser Than You Think

How old is that sponge you're using to clean your dishes? Oh, and to wipe down your counters? And to sop up spilled messes — boy, it truly is an all-purpose tool, isn't it? If you can't remember (or even if you can), it's probably time to toss it and use a new one. That's because, according to the first comprehensive study on the topic, your kitchen sponge is disgusting. And the only way to fix that is by throwing it out and starting fresh.

Can You Smell What Your Sponge Is Cookin'?

For a study published in the Nature journal Scientific Reports, researchers led by Markus Egert of Furtwangen University in Germany sequenced the microbial DNA in 14 used kitchen sponges to figure out exactly what kind of bacterial situation they had on their hands. They also tagged breeding microbes with fluorescent markers so they could watch them using special imaging techniques.

They hit the motherlode: Out of more than 223,000 DNA sequences, the sponges came back with 362 different types of bacteria. In fact, they found that a single cubic centimeter could be packed with more than 5x1010 bacteria; that is a density the scientists say is only found in feces.

Most of the bacteria weren't harmful. You're surrounded by bacteria every second of the day, after all. The samples were dominated by the bacteria Moraxellaceae, which is found all over human skin and kitchens. It's responsible for the sour smell of laundry (and of old sponges, who knew?).

But some of the bacteria was harmful. Five of the 10 bacteria most commonly found in the sponges were potential pathogens. Even worse, those nastier bacteria were found in higher percentages in sponges that had been regularly sanitized. That makes sense when you think about it: If popping a sponge in the dishwasher or microwave kills 99 percent of the bacteria festering within it, that remaining 1 percent is by definition the toughest bacteria on the sponge — and now it's free to take over.

What's a Sponge Lover to Do?

So now that you're thoroughly grossed out by that moist little rectangle moldering by the sink, what do you do about it? The obvious-but-difficult option is to stop using sponges altogether. Your dishwasher successfully kills far more bacteria than hand-washing can, if only because it can use hotter water than your skin can stand. As for countertops and general messes, disposable antibacterial wipes could do you good (apologies to Mother Earth for the waste).

But these suggestions all assume you have a home with a dishwasher and the disposable income for disposable wipes. If you don't, go with what the study authors say. "We ... suggest a regular (and easily affordable) replacement of kitchen sponges, for example, on a weekly basis." Next time you find yourself giving a sponge the sniff test, remember the old adage: When in doubt, throw it out.

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Learn about the surprisingly complex world of germs in "Good Germs, Bad Germs: Health and Survival in a Bacterial World" by Jessica Snyder Sachs. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Ashley Hamer September 6, 2017

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