Stop Cleaning Your Kitchen Sponge!

For most of us, the thought of sanitizing our kitchen sponges never crossed our minds. And that’s probably a good thing.

Scientists from Germany recently reported what they found living inside kitchen sponges. They took samples from 14 used kitchen sponges and extracted DNA. What they found was an astounding 54 billion bacteria cells per cubic centimeter of sponge.

Image credit: Horia Varlan.

While most of the bacteria found are not harmful to humans, the researchers did find bacteria such as E. coli, and Klebsiella and Moraxella species in the sponges. Kitchen sponges also have the second highest amount of coliform bacteria (bacteria that serve as indicators for fecal contamination) in the whole house. When we thinking about fecal bacteria, the toilet is first to pop into mind. So are coliform bacteria found in the highest quantity in the bathroom? No. It’s actually sink drain traps.

The scientists also investigated whether sanitizing sponges is worth the effort. Surprisingly, they found that boiling or microwaving sponges doesn’t help at all. Bacterial numbers don’t seem to change before and after sanitization and to make matters worse, sanitization efforts actually backfire: pathogen-related species make up a higher proportion of total bacteria after sanitation. This happens possibly because sanitizing the sponges kills some bacteria and that pathogenic bacteria, which may be more likely to resist sanitization efforts, take over.

Confocal microscopy of a sponge sample. Red regions represent bacteria and cyan represents the sponge. Image credit: Cardinale et al.

The solution to this problem? The researchers recommend replacing the sponge every week. However, the scientists who performed the study also pointed out that they were not aware of any incidence of infections with sponge bacteria as the culprit.

As for me, I think I’m going to clean some dishes with my old kitchen sponge right now.

CC BY-NC-ND 4.0 Stop Cleaning Your Kitchen Sponge! by Jennifer Tsang is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.


  1. // Reply

    We now understand the importance of building and sustaining a healthy human microbiome, but at the same time we increasingly understand the importance of hygiene in the community – not least as a means to reduce antibiotic prescribing. The question is then -“how do we best protect against infection whilst re establishing our connection with the microbial world we live in”. The answer lies mainly in lifestyle changes e.g returning to natural childbirth, outdoor activity, less antibiotics, better diet – but also in “targeted hygiene”. This means focussing on breaking the chain of infection by intervening in the places and at the time that matter – with an effective intervention. The key “places that matter” are our hands, hand contact and food contact surfaces – and cleaning cloths/sponges – these are the “superhighways” for spreading germs from infected sources which are mainly people, food and domestic animals. Cloths and sponges are critical control points – using a sponge to spread the resident microbes increase the risks of spreading pathogens. There is very good evidence of how pathogens are spread via cleaning cloths in numbers sufficient to cause infection – proving that an infection outbreak was caused by the hands or by a sponge of whatever is just not possible. In the last 12 months I have seen messages from allergists, nutritionists, microbiomists etc exhorting us to “stop washing our hands”, stop using the dishwasher and hand dish wash instead – and now using kitchen sponges to spread good germs. We need to do proper risk: risk assessments before making these recommendations. Read more about targeted hygiene at

    1. // Reply

      Hi Sally, thanks for your insight. The authors are suggesting it’s best to throw out your sponge than to try to sanitize it as sanitizing it actually increases pathogen load (compared to before it was cleaned) when the sponge is recolonized by bacteria. Until we find a better way to sanitize the sponges, the only thing we can do to prevent spread of pathogens is to toss it. They certainly aren’t advocating using kitchen sponges to spread “good germs” and I hope others aren’t promoting that!

      1. // Reply

        I absolutely agree, based on the data I have seen, that it is very difficult to sanitize sponges – and I think considering their potential for picking up and spreading pathogens, this warrant the expense involved in “tossing it. But the author of the piece above does not seem to agree because she says “As for me, I think I’m going to clean some dishes with my old kitchen sponge right now”

        We are seeing an outbreak of norovirus at the world athletics which seems to be due to person to person transmission – and one wonders whether and to what extent cleaning cloths etc are a factor in the rapid spread of the virus which can occur through hotels

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