Thinking of Disinfecting Your Sponge? It’ll Do More Harm Than Good

Common house-cleaning wisdom advises you to clean your sponges periodically. Some experts advise running them through the dishwasher, while others suggest microwaving a wet sponge. But a new study says that both of those techniques will do more harm than good, as The New York Times reports.

A trio of microbiologists came to this conclusion after collecting used sponges from households in Villingen-Schwenningen, Germany, a city near Zurich. As the researchers write in Nature Scientific Reports, they asked the 14 houses that gave them sponges to describe how they were used—how many people in the house handled them, how often they used them, how often they replaced them, and if they ever tried to clean them.

Analyzing DNA and RNA found on those sponges, they found a total of 362 different bacterial species living on them. The sheer number of the bacterial colonies was staggering—some 82 billion total bacteria were living in a cubic inch of sponge. (As co-author Markus Egert told the Times, that’s similar to what you’d find in your poop.)

As the researchers discovered by analyzing the bacteria found on sponges whose users said they regularly cleaned them, disinfecting a sponge using a microwave, vinegar, or a dishwasher is worse than useless. It seems that when you attempt to clean a sponge, you kill off some bacteria, but in doing so, you provide an environment for the worst species of bacteria to thrive. Sponges that were regularly cleaned had higher concentrations of bacteria like Moraxella osloensis, which can cause infections in humans. (Though it’s unclear how likely you are to get infected by your sponge.) It’s also the reason dirty laundry smells. By microwaving your sponge, you’re probably just making it smellier.

Sadly, there’s not much you can do about your dirty sponge except throw it away. You can recycle it to use as part of your cleaning routine in the bathroom or somewhere else where it’s far away from your food, but the best way to get a clean sponge, it seems, is to just buy a new one. May we suggest the Scrub Daddy?