Ask people to name the dirtiest place in their home and most will point to the toilet. In the kitchen, the usual suspects are the trash can or the floor under the fridge. Microbiologists who have swabbed real kitchens keep finding the same winner, and it’s the one object people use specifically to make things clean. It sits by the sink, it’s damp almost all the time, and it touches every plate, pan and counter in the house.
It’s the kitchen sponge.
What the studies found
When NSF International, a public health organization, asked volunteer families to swab 30 everyday items in their homes, dish sponges and dish rags came out on top: around three-quarters of them carried coliform bacteria, the family that includes E. coli and Salmonella. The kitchen sink came second, followed by countertops and cutting boards. The bathroom items people expected to be worst ranked lower.
A 2017 study published in Scientific Reports went further. German researchers analyzed used kitchen sponges and identified 362 different kinds of bacteria, at densities of up to tens of billions of cells per cubic centimeter, some of the highest bacterial concentrations found anywhere outside the human gut.
Why the sponge is the perfect breeding ground
A sponge combines everything bacteria need: warmth, constant moisture, food residue and an enormous internal surface area of tiny pores to live in. Wiping a counter with a dirty sponge doesn’t clean it so much as redistribute what’s in the sponge across the surface.
How to keep it from becoming a problem
- Rinse it thoroughly after each use, squeeze it out and let it dry in an open spot, not in a puddle by the sink.
- Sanitize it regularly: running it through the dishwasher, or microwaving it while damp for about a minute, kills most bacteria. Make sure it’s wet and contains no metal before it goes in the microwave.
- Replace it often. The 2017 study found that regularly sanitized sponges didn’t always end up with fewer bacteria, so the authors recommended swapping sponges out about once a week rather than trying to clean them indefinitely.
- Use separate sponges or cloths for dishes and for counters, and never use the dish sponge to wipe up raw meat juices.
If you’d rather move away from sponges altogether, dish brushes are a good alternative: their bristles dry quickly and they can go in the dishwasher. Washable cloths work too, as long as they’re swapped for a fresh one every day or two and washed hot.
The runners-up
The sink deserves a scrub with hot, soapy water a few times a week, drain included. Cutting boards should be washed in hot water after every use, with separate boards for raw meat and produce. And the cutlery drawer, where crumbs and moisture collect unseen, benefits from being emptied and wiped out now and then, which is also why some people line it with foil every fall.
The thing you clean with needs cleaning most of all. Dry it, sanitize it, replace it every week. That’s the trick.
