You're probably not doing it often enough.

Whether you’re wiping off the counter or scrubbing a pot, maybe you reach for a versatile kitchen sponge to do the job. Chances are, you aren’t cleaning that handy cleaning tool as much as you should.

The kitchen sponge is the germiest place in the home, according to a 2011 study from the National Sanitation Foundation. When researchers had people in 22 households swab 30 different surfaces in their homes, they found that 77% of dish sponges or rags had coliform, which is a bacteria family that includes salmonella and E. coli. By comparison, only 5% of toilet seats had coliform.

“The biggest misconception identified through the study was that the bathroom is the dirtiest place in the house when in fact the kitchen had the most germs,” the researchers wrote.

Why a Kitchen Sponge Is a Microbe Magnet

Kitchen sponges are porous and damp, which creates the ideal environment for bacteria to grow.

“Sponges have a physical structure that consists of an array of large and small holes, and this gives sponges the ability to hold water,” says Zahra Mohammad, Ph.D., a food microbiology and safety expert with the University of Houston and the American Society for Microbiology.

“That means the sponges always stay moist, and water won't be released until someone forces it out by squeezing or drying out over time. In addition, food residues easily go into the sponge.”

That wet, food-filled sponge becomes the perfect place for bacteria to grow quickly. Billions of bacteria can grow in sponges, says Mohammad, but not all of them are dangerous.

Harmful bacteria—or pathogens—like salmonella, E.coli, and listeria can grow quickly and spread from sponges to hands, kitchen surfaces, and other equipment. Depending on the surface and type of bacteria, they can linger for days and make people sick.

How to Clean Your Kitchen Sponge

You should clean your kitchen sponge thoroughly and often. Soak the sponge for 5 minutes in a solution of one-quart water and three tablespoons of chlorine bleach, suggests Jessica Ek, spokesperson for the American Cleaning Institute. Then let the sponge air-dry.

Mohammad prefers using the microwave. She zaps it on high for a minute.

“Some people asked me whether bacteria can spread from the sponge and contaminate the microwave. Do not worry, this is not the case as all bacteria will be gone,” she says. “Other experts recommend using a washing machine with a dry cycle. But I would say, the microwave is faster and more effective.”

Mohammad microwaves her kitchen sponge twice a day. Ek suggests cleaning the kitchen sponge at least once a week.

How Often You Should Replace Your Kitchen Sponges

Even if you are religious about cleaning your sponge, you still need to replace it often.

The USDA says that microwaving or boiling kitchen sponges “may reduce some of the bacterial lode,” but that’s not enough to avoid cross-contamination with your hands, counters, or food. If you use sponges, buy new ones frequently, that agency advises.

Mohammad throws away her kitchen sponge every week and uses a new one. She sometimes replaces it sooner if it is dirty. Ek says a kitchen sponge should be replaced at least every 2-3 weeks, “depending on how frequently and roughly you use it.”

Sponge Alternatives to Consider

If the germ factor has turned you off sponges, there are other, cleaner options like Swedish dishcloths which act like washable, sturdy paper towels. They dry quickly so bacteria isn’t as prevalent.

Kitchen brushes may also be a cleaner way to scrub your dishes. Several recent studies have found that bacteria grow and thrive better in sponges than kitchen brushes because brushes dry faster than sponges and may be less of a friendly environment for germs.

“Many brushes are also dishwasher safe and last longer than sponges when properly cared for,” says Ek, who suggests using paper towels to mop up spills.

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