We've all done it: After scrubbing some dishes, maybe a fork or two, you drop a sopping wet sponge into the kitchen sink – plop – and leave it there until later.
It's one of the grossest mistakes made in the home, science suggests. Kitchen sinks have been shown to be filthier than toilets, providing damp playgrounds for fecal bacteria (think E. coli) and other germs that attach to your sponge.
"Sink surfaces, particularly near the drain, tend to be a major collection area for bacteria and biofilm development," said Kelly Reynolds, a University of Arizona public health researcher who notes that "consistently moist areas are more prone to bacterial growth."
Indeed, a 2017 study found sinks and sponges are huge harborers of fecal bacteria in 44% of homes. In the study, published in the peer-reviewed Journal of Food Protection, 15% of homes tested positive for E. coli – mainly in kitchen sinks
Why? Perhaps because kitchen sinks are not only frequently damp but frequently touched, an earlier study noted in 2008.
Tests of 15 family's kitchens found "the kitchen was more heavily contaminated than the bathroom, with the toilet seat being the least-contaminated site," according to the study in the peer-reviewed Journal of Applied Microbiology.
As Reynolds told Buzzfeed, most people disinfect their toilets far more than their sinks, where leftover food particles can mingle with bugs from raw meat and our own poorly washed hands. Sponges soaking in that environment hardly stand a chance.
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A small study of 14 used sponges by researchers in Germany revealed 362 types of bacteria, with potentially pathogenic germs among those most commonly found. That 2017 study, published in the peer-reviewed Scientific Reports, described sponges as "microbiological hot spots" that should be replaced every week.
Don't want to ditch a sponge weekly? There are alternatives.
First, sponge wisely: Never mop up raw meat juices with one, as Jennifer Quinlan, a Drexel University microbiologist, told NPR. Opt for paper towels instead.
And store sponges in a place where they can dry out – a basket or rack, say, instead of a sink bottom – to reduce bacteria, Reynolds said. That won't eliminate all the germs, she said, but exposure to high heat can help, too.
Pop a wet sponge into the microwave for one minute or put it in a dishwasher set to run with a drying cycle each day, the Academy of Nutrition and Dietetics recommends, and throw out sponges once they look used or start to smell.