Germs thrive in kitchen sponges much longer than we think and not even a smell will clue you in, new study shows

Kitchen sponges are well known to harbour germs between uses, but now a new study has revealed the bacteria remains much longer than we first thought and not even a bad smell will clue you in.

The German study, which was published in the Journal of Food Protection looked at the potential for Salmonella, E. coli and Staphylococcus to survive and grow in sponges and easily transfer to surfaces over a period of 14 days. 

Researchers found the bacteria, which is known to cause food-poisoning, remained even once the sponges dried out.

“All three pathogens persisted within the sponge matrix for at least two weeks, even at very low initial populations,” the researchers said.

The study revealed these germs can transfer to other kitchen surfaces, like a bench, with only mild pressure, raising concerns for cross-contamination when wiping with sponges. Researchers concluded that this makes sponges even more germ-riddled than sinks and chopping boards.

“Our findings emphasise that pathogen persistence in sponges creates a substantial risk of cross-contamination. Once bacterial populations reach a critical density, contaminated sponges can transfer pathogens to surfaces such as cutting boards and countertops. Subsequent contact of these surfaces with food may realistically lead to transmission to consumers,” they said.

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Unfortunately, the famous sniff test is no help in figuring out whether your sponge is harbouring bacteria as the study also found that odours didn’t correlate with the number of germs in the sponge. Discolouration and sliminess aren’t associated with bacteria levels either.

So what does this mean for cleaning dishes and the kitchen bench?

Well, if you want to continue using a sponge you should replace them much more frequently and clean them by boiling, microwaving, soaking in bleach or running through a dishwasher cycle. You should also use paper towels for raw meat juices and disinfect that surface afterwards.

“If you’d rather stick with a sponge, the best way to keep bacteria levels down is to spray it with disinfectant periodically throughout the day and swap it for a new one every week,” Primrose Freestone, Senior Lecturer in Clinical Microbiology at the University of Leicester, wrote in an article for The Conversation.

Sponges are also an environmental problem given that they are often made from plastics, which means they take a long time to break down in landfill and shed microplastics when they’re used.

The easy solution for that if you prefer sponges is to switch to biodegradable options, like those made from cellulose and loofah.

However, an alternative solution is to use dish brushes. A study from 2022 by researchers in Portugal found lower bacteria and that Salmonella died faster in brushes than sponges.