Aunt Monika votes Green. Out of conviction, because in her view it is the only party that actually does something for the environment. Aunt Monika also lives in a very environmentally conscious way. She eats only organic food because of pesticide residues, and when it comes to meat (“vegan would be better,” she sighs, “but I just can’t give it up”), she also insists on organic products because of animal welfare and antibiotic residues. After all, she doesn’t want to get sick. She is equally consistent in other areas: she practically no longer uses the dishwasher (“too much water, too many chemicals, rinse aid, salt, and who knows what’s in those detergent tabs!”). She washes dishes with a sponge. And because she is frugal, she uses her dish sponge for a very long time — until the green scrubbing side is completely worn away.

There is little point in arguing with her. I look at the sponge and think of a study published in 2017. It came from the laboratory of Dr. Markus Egert, Professor of Microbiology and Hygiene at Furtwangen University, and bears the harmless title “Microbiome analysis and confocal microscopy of used kitchen sponges.” But the paper is anything but harmless.

Egert and his team found that kitchen sponges left slightly damp beside or in the sink — like Aunt Monika’s (the very same sink in which she washes dangerous pesticide residues off her fruit and vegetables) — contained around 54 billion bacteria per cubic centimeter. That is six times more microbes per cubic centimeter than there are people on Earth, and almost exactly as many as are found in human feces.

And what kinds of bacteria! The researchers identified 362 different species, including a whole host of pathogens: Salmonella and Staphylococcus, strains of Campylobacter, Enterobacter cloacae, Escherichia coli, Klebsiella, and Proteus. These can cause diarrhea, blood poisoning, pneumonia, wound and skin infections, urinary tract infections — many of them are notorious causes of hospital-acquired infections.

These microbes thrive in sponges: the cavities provide ample space for colonization, leftover food supplies plenty of carbohydrates, fats, and proteins, the dishwater creates a comfortable temperature, and the environment remains constantly moist because no sponge ever dries completely between uses. Most of the time, the sponge is also used in between washing dishes to quickly wipe down a surface.

Every time Aunt Monika does this, she spreads bacteria across the kitchen counter, onto her hands, and onto everything she touches afterward. And of course, via the sink, onto the fruit and vegetables she is trying so carefully to wash clean and healthy.

As early as 2011, the U.S. National Science Foundation found that the kitchen is the least hygienic place in a home — not the bathroom or toilet, but the kitchen, led by the kitchen sponge, followed by the sink, countertops, and cutting boards. Bathroom items only came afterward. It was no coincidence that Prof. Andreas Hensel, head of the German Federal Institute for Risk Assessment, put it very bluntly in a 2017 interview: “A carrot that accidentally falls into the toilet while you are peeling it can usually still be eaten. But if it falls into the sink, you’d better not take a bite.”

To disinfect the sponges, neither boiling water nor heating them in the microwave is sufficient. Egert’s team found that while these methods kill many bacteria, some survive — and this effectively breeds especially robust strains. Worse still, it selectively concentrates pathogenic strains because they are naturally more stress-tolerant.

The hygienist recommends using sponges for no longer than one week before replacing them. Norwegian microbiologists go one step further and advise switching to dish brushes altogether. Some already come with antibacterial bristles. But even conventional brushes are better than sponges: they offer less surface area for bacteria and dry relatively quickly when hung up after use. Better still, simply put them in the dishwasher together with the dirty dishes. Afterward, they are germ-free.

Aunt Monika thinks all of this is nonsense. After all, she has been doing things this way for decades. And because she eats only organic food, she says she has a strong immune system.

“You just want to distract from the toxic residues, which are a huge danger to health!” I point out that she also has a liver. But she dismisses the argument. “Yes, but it only knows how to deal with natural toxins — artificially produced chemicals are foreign to it.” But that is another topic.