Quick — what’s the germiest room in the house?
You might be surprised to learn that it’s not the bathroom. Microscopic bugs and bacteria actually favor the kitchen, where you eat and prepare food. And the nexus of all that microbial activity could be sitting right next to the kitchen sink: on the sponge. If you’re washing dishes by hand, your cups, plates and flatware may not be as clean as you think.
In a 2017 study published in Scientific Reports, German researchers did a germ-analysis of kitchen sponges with some startling results. There were 362 different kinds of bacteria lurking in the crevices of sponges they collected from ordinary homes, in astounding numbers — up to 45 billion per square centimeter. (That’s about the same amount found in the average human stool sample.) Considering the size of a typical dish sponge, that’s nearly 5.5 trillion microscopic bugs crawling around on the thing you use to “clean” your dishes.
That amount even surprised the researchers conducting the study. “It was one to two orders of magnitude more than we initially expected to find,” says Markus Egert, professor of microbiology and hygiene at Furtwangen University, who led the study. When Egert and his team visualized the bacteria under the microscope, the 3D impact was even more alarming. “No one had ever seen bacteria sitting inside a sponge,” he says. “One problem we have with bacteria and microbes is that we cannot see them. And if you don’t see them, you don’t believe they are there.”
Here are the nasty secrets of your kitchen sponge — and what you should use to wash your dishes instead.
Why you shouldn’t use a sponge
The ideal way to sanitize dishes and cups is to run them through the dishwasher. Since a dishwasher cycles both hot water and hot heat during the drying phase, it’s an effective way to get your eating utensils clean. But it’s important to use the full energy cycle to get the best results. Energy savers use less energy and therefore generate less heat for sanitizing. (The heat is important to destroy the microbes.)
If you don’t use a dishwasher, you’re likely to choose a kitchen sponge. But sponges are ideal breeding grounds for bacteria, given the amount of food residue that can stick on and inside the porous surfaces, and the numerous moist havens that lure the bugs and provide fertile ground for them to breed. “The sponge never really dries,” says Leslie Reichert, a green cleaning expert and author of Joy of Green Cleaning. “It’s the perfect environment for bacteria…you never totally rinse the food out of the sponge.”
The good news is that the bugs residing in these sponges aren’t generally the ones that can make you sick. Egert did not find the common bacteria that cause foodborne illnesses, such as salmonella, E. coli and campylobacter. Still, it’s possible that these disease-causing bugs were simply overwhelmed by the sheer number of other bugs; Egert suspects that if researchers look hard enough, they would find them in some sponges.
The better way to hand wash your dishes
Use a plastic or silicone brush. Brushes tend to stay drier when they’re not used, and they don’t have as many deep crevices as sponges where water and bacteria can grow. “You can stand brushes up, or put them in a caddy where they are likely to dry out,” says Carolyn Forte, director of the home appliances and cleaning products lab at Good Housekeeping Institute. “The material is not as porous as a sponge is, and if something is stuck to the brush, you can see that and rinse it out.” They’re also easy to clean; you should run them through the dishwasher once a week or so.
How to clean a sponge
If you insist on using a sponge, you should make peace with frequently cleaning it and throwing it out.
Simple soap and water won’t cut it. In Egert’s study, sponges that were cleaned this way harbored more bacteria. These microbes were more likely to be the kind that are more resistant to detergents since they survived the cleaning, and they could potentially cause harm to human health. In other words, if you clean your sponge the wrong way, you’re selecting for the nastier bacteria. “Improper cleaning may make the situation even worse,” he says. “Cleaning, especially by non-cleaning experts at home, usually does not clean all the bacteria inside because there is such a large amount of microbes. Some survive, and become more resistant; if you do this a couple of times, you might select for more pathogenic communities.” That’s why Egert recommends changing kitchen sponges weekly to avoid bacterial buildup.
Still, “it is possible to clean sponges,” says Forte. House-cleaning experts advise that you to sanitize dish sponges every few days in a variety of ways, from soaking it in a bleach solution to zapping it in the microwave or running it through the dishwasher.
Good Housekeeping compared these three methods and found that the bleach and water solution worked best in removing 99.9% of salmonella, E. coli and pseudomonas bacteria they added to test sponges. They created a solution of 3 tablespoons of bleach to a quart of water and soaked the germy sponges for five minutes, then rinsed them out.
The next most effective method was microwaving. It didn’t kill as many E coli as the bleach method, but still destroyed enough to sanitize the sponges. Forte says it’s important to wet the sponge thoroughly before zapping, to prevent it from catching fire in the microwave. It’s also important to thoroughly dry the sponge before using it to wash dishes again, since the dampness could attract more bacteria.
Throwing the sponge in the dishwasher was the least effective cleaning strategy of the three, although the machine wash did kill 99.8% of the bugs. If you opt for this method, make sure you don’t use the energy-saving option.
You can also choose a sponge that isn’t made from paper or wood pulp, which is what’s used to make traditional cellulose sponges. Many are now made from plastics that are less porous and absorbent, and therefore less likely to retain the moisture that attract bacteria. Reichert also recommends plant-based foam sponges infused with a citrus cleaning solution that keeps bacteria at bay for about a month.
What to do with your dirty old sponge
If throwing out sponges frequently seems wasteful, Egert suggests using them in other parts of the house where bacteria might not be so important, such as cleaning floors or gardening equipment. As long as the germy sponges aren’t being used on the dishes, glasses or flatware that you eat with every day, your sponge shouldn’t cause problems.