How Often Should You Replace Your Kitchen Sponge?

old kitchen sponge — Your kitchen sponge can harbor some gnarly stuff if you don't replace it enough. logistock/Shutterstock

Take a look at your kitchen sponge and what you ask it to do all day. It cleans the dishes, sure, but it probably also wipes down the counters, cleans up crumbs on the table and gets jelly off your kid's face.

While washing all those other things with soap and warm water, the sponge itself gets washed, too, right? Not really, no.

There Are Germs in Your Sponge

All those little holes in the sponge (they're called ostia) can harbor food and germs, and the warm water can help them grow. One study published in Scientific Reports found up to 45 million bacteria in 1 square centimeter (0.1 square inch) of a kitchen sponge. Those 45 million were made up of 362 different species of bacteria, though most of those aren't the kinds of germs that make people sick.

Another study by the National Sanitation Foundation found that 77 percent of sponges had coliform bacteria, a fun little family of bacteria that includes salmonella and E. coli. Compare that to the 5 percent of toilets in the same households in this study that had coliform.

To put it scientifically, yuck.

When Is It Time to Toss That Sponge?

cleaning with sponge — When you're cleaning surfaces like your kitchen counters, you want to be sure your sponge isn't spreading around nasty germs like salmonella and E. coli. kate3155/Shutterstock

Most experts, including Martha Stewart, advise tossing your kitchen sponge after a week — two weeks at most.

How can you tell if your sponge needs to go? Easy: Look at it and smell it. If you can see or smell bits of food, or the remains of a spill you wiped up the day before (or a week before) that sponge has got to go.

You may have heard that microwaving a sponge can kill germs, but the U.S. Department of Agriculture (USDA) says that's not good enough. It just doesn't kill all of the bacteria, and the remaining germs can continue to replicate in the sponge.

Cleaning a Sponge

If you want to try squeezing a few more useful days out of your sponge, here's how to clean a sponge:

Microwave a wet sponge for two minutes.
Run the sponge through the dishwasher on the top rack, including the dry cycle.
Soak the sponge in a solution of 1/2 teaspoon of bleach in 1 quart of water.

While it's possible to clean a sponge, the safest answer is to toss out the old and wring in the new.