Your Kitchen Sponge is Covered With Bacteria — Don’t Bother Cleaning It

By Nathaniel Scharping | July 31, 2017 3:34 pm
(Credit: Africa Studio/Shutterstock)

(Credit: Africa Studio/Shutterstock)

If bacteria all glowed the way some bioluminescent species do, you’d probably go blind walking into your kitchen. An abundance of organic material and damp surfaces allows microbial life to flourish around spaces where food is prepared, but one particular item shines brightest in the bacterial firmament. It’s the kitchen sponge, that workhorse of culinary clean-ups, and it is absolutely overrun with bacteria.

Kitchen sponges have been picked out as bacterial strongholds for quite a while, though that hasn’t stopped new studies from surfacing. Each fresh revelation of microbial infestation spawns a new round of horrified media coverage, as every study seems to add to the list of potentially deadly diseases lurking in our households. The latest insights come from a team of researchers in Germany who use genetic sequencing to compile the most comprehensive list of sponge bacteria to date.

Deadly Sponges

The results aren’t surprising, but they are illustrative of just how tenacious household bacteria are. Looking at 14 different used kitchen sponges, the researchers found up to 54 billion bacteria per cubic centimeter, spanning 118 genera. Many of these pose no harm to humans, it should be said, but among the species the researchers also found varieties of E. coli, Klebsiella, Staphylococcus, Salmonella and others implicated in food-borne illnesses. They found that the bacteria appear most often on the surface and visible cavities of the sponge, and their analysis indicated rapid growth.

In a paper published in Nature Scientific Reports, the German researchers were able to expand the list by taking advantage of new developments in gene sequencing technology, which they paired with a type of high-precision imaging. Most previous studies relied on cell cultures grown from samples, which don’t always pick out the full range of bacterial life on sponges. Many of those also used only a single sponge for their analysis, compared to over a dozen here.

Don’t Even Bother

The study comes with another, more provocative claim as well: cleaning sponges doesn’t seem to help at all. Based on previous studies, conventional wisdom held that microwaving or boiling sponges helped to kill off bacteria. When they attempted to replicate these findings with their own sponges, the researchers found very little difference in terms of bacteria numbers between sponges that had been cleaned and those that hadn’t. The cleaning did seem to alter the composition of the bacterial population, though, shifting it toward Moraxella and Chryseobacterium, both of which can cause disease. This likely happens because the sanitization kills some species of bacteria but not others, allowing the survivors free rein to spread and grow.

The best option, the researchers say, is to simply replace your sponges regularly, on the order of once a week. More studies of kitchen sponges are still needed as well, to explore how dangerous the bacteria on sponges actually are (especially given that there are no recorded cases directly linking sponge bacteria to an infection), find better sponge sanitation methods and more fully explore the “sponge microbiome.” The field of sponge science is alive and well.

CATEGORIZED UNDER: Health & Medicine, Living World
  • Uncle Al

    An Oxford comma-challenged assistant prof saw Mythbusters Episode 135 and thought ”tenure!”, right?
    Youtube v=dQgVn3AvJ8A 4:10ff,

    DOI:10.1128/AEM.07816-11 Invading Space Navy slugs from the Star Nebula will be themselves invaded by all-American commensalist slug-parasitic nematodes, bacteriolyzed, liquefied, and chugged like a cloudy odorous frankly repellent salt-rimmed frosted glass of Lost Hippo Face Plant open-fermentation beer. Sponge-worthy 54 billion cells/cm³ Moraxella osloensis, we love you.

    • Kamran Rowshandel


  • darryl

    Sigh, if it’s not pathogenic, then it’s a non story. I have to imagine the microwaving/dishwashing/boiling would kill off the pathogens – or you know, the soap.
    On a side note, one could also pressure cook to kill off the spores.


    • Not_that_anyone_cares, but…

      Indeed, a pressure cooker may be the only reasonable way to kill off the spores.

    • Tony Fyffe

      some were pathogenic. it says right up there.

      • darryl

        Even if they are pathogenic, is there any evidence that anyone has gotten sick as a direct result of the pathogens in the sponges?


  • Jan

    Once a week? Think of the landfill.

  • September Autumnleaf Meadows

    I live alone so only replace my sponge once a month. In the middle of the month I let the sponge soak overnight in a bowl of acetone. That seems to sanitize it fairly well.

  • Not_that_anyone_cares, but…

    “…More studies of kitchen sponges are still needed… (especially given that
    there are no recorded cases directly linking sponge bacteria to an

    I was thinking something along this line of reasoning. More like ‘More studies of kitchen sponges are NOT needed.’

  • JohnnyMorales

    “More studies of kitchen sponges are still needed as well, to explore
    how dangerous the bacteria on sponges actually are (especially given
    that there are no recorded cases directly linking sponge bacteria to an

    Uh NO, Just NO. The answer is obvious.

    That there are no recorded cases directly linked after people literally using bacteria laden sponges literally trillions and trillions of times collectively by all of humanity in their kitchens since sponges started to be used for that purpose, it’s extremely clear there is no real danger, and is absolutely not worth researching to find out if there is.

    And if there were in the many decades (centuries if you include natural sea sponges) any danger, IT WOULD have been documented by now if there were even a slight risk even if no one ever looked for it, simply to the sheer number of times people have used bacteria laden sponges.

    • Tony Fyffe

      so, lack of evidence means it doesn’t exist? Uh, NO, Just NO.

      Do you think every instance of hospitalization due to food-born illness would necessarily be attributed to a sponge as opposed to the food?

      The study found salmonella in sponges, and we know salmonella causes illness. If someone got salmonella poisoning from a sponge, they probably attributed it directly to the food as opposed to the sponge, because no-one has ever heard the term “sponge-born illness (yet).”

      The food could cross contaminate the sponge, the food could be thoroughly cooked, killing all salmonella in the food, then when they used the cross-contaminated sponge to wash a glass and drink from it, they got salmonella, which everyone associates with food more than sponges (until now), so when they went to the ER, they said “It must have been the food.”

      Lack of evidence doesn’t imply lack of existence.

      You go ahead and use sponges, and I’ll continue not to eat off of your dishes.

      • Tayvl

        How, pray tell, can the salmonella attach to the dishes? It certainly could if you just wiped with the sponge without soaping or rinsing, but who does that? BTW, do you use fresh towels every time you dry your hands? (I use paper towels, to jump ahead a bit…)

      • Jose C. Castillo

        I like the reply: “Lack of evidence doesn’t imply lack of existence”

    • Jose C. Castillo

      “The latest insights come from a team of researchers in Germany who use genetic sequencing to compile the most comprehensive list of sponge bacteria to date”

  • thekemmlers

    I’ve seen photomicrographic videos that show kitchen counters are likely just as bad. Just add water and the microbial population explodes, even if disinfectants are used in the water. Apart from the well-taken question of whether the microbes at issue are pathogenic, a partial solution is to squeeze the sponges enough that they can dry out when not being used.

    • Tony Fyffe

      the study did find multiple pathogens.

    • Marty G

      Why use sponges at all? I use a plastic bristled brush with soap and rinse thoroughly. The brush tends to dry completely between uses, and as Tayvl noted above, if the dishes and utensils are rinsed thoroughly, what is the problem anyway? If they tested the dishes and utensils for bacteria there’d be no breathless terrifying headline, would there? No one eats off their sponges.

  • Tayvl

    This would be a problem if one didn’t use soap or detergent. The sponge merely knocks the debris off that’s been loosened by the soap. Once you rinse with clean water, everything gets removed. Try testing the items washed for bacteria instead of the sponge or washcloth. Nobody eats off of their kitchen sponge…

    • Tony Fyffe

      that’s not how that works. they literally found 50 billion bacteria per cubic centimeter, 80 billion bacteria per cubic inch. they didnt get removed by rinsing with water, or by disinfecting.

      • Tayvl

        Yes, and they don’t need to be removed because you don’t eat off your sponge. Those bacteria don’t attach to the dishes/utensils being washed, they either stay on the sponge or go down the drain with the rinse water. The only way you could transfer them to your dishes would be to wipe the dishes down with the sponge while not using soap or rinsing them off.

        • Tony Fyffe

          so, at first you claim they can’t stick to sponges, when i point out they do, now you claim they can’t stick to dishes. if they can’t stick to dishes, then dont wash them at all. nothing will be able to grow, according to you.

          so, i don’t have the time, energy, or desire to teach you science from the ground up, but if you’d like to google some real science for yourself, try the search terms “bacterial attachment, methods of bacterial attachment, can bacteria stick to smooth surfaces, how can bacteria stick to tooth enamel, how can bacteria stick to heart valves against the flow of blood with each pump of the heart, etc, etc.

          Now, go science!

          • Tayvl

            You misunderstood my original comment. I said the bacteria don’t stick to the utensils because they’re rinsed off. There’s no point in checking the sponge for bacteria. Wonder why they didn’t also check the items washed by the sponge? Because then they wouldn’t have a scare story for people to click on…

          • ICBM904

            Your statement was perfectly clear. You didn’t say anything about bacteria not sticking to sponges.

          • BadTigz

            The problem is the article took away the wrong information from the data and the writer did not look at the documentation for the study…only the results.
            the two dangerous microbes they found? Was only in a hand full of sponges. Second, all the bacteria that remained after sanitizing? all of them inert and won’t cause disease in a healthy person. (of course if you have an immunocompromised patient in your house, you want to be a lot more careful – with everything, not just your sponges)
            Secondly, did you realize that you have over 30 million bacteria in 1 sq inch surface of human skin? Oily areas (like the face) have up to 500 million bacteria per sq inch of surface area. (I don’t even want to think about arm pits and groin area)
            Yup, that is your own dirty filthy body. Just rubbing your finger across a dry plate will deposit more virus and bacteria than washing a plate with soap and a sponge and rinsing it off with water.

            You’ve been duped by scare tactics dude, and you took it hook, line, and sinker.

  • EricNYC

    “replace sponges once a week.”
    “This article was brought to you by the makers of sponges.”
    How bout using dish rags and *washing them* once every week. Same germ exposure, 1/50th the cost.

  • Bob Reynolds

    Acetone does not kill bacteria – bleach however does but not all

  • Kamran Rowshandel

    What about bleach?

  • Bill Branch

    Sponge problems vanish if you use a standard dish soap sold in tubs at Latino markets such as Axion. These soaps contain vinegar or citrus juices and the bacteria die in an acid environment. Just leave the sponge in the tub of soap with enough water to keep the sponge wet.

  • AZDiver

    I have yet to be convinced that microwaving doesn’t kill bacteria. Why wouldn’t it?


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