Kitchen Hygiene: Let’s Talk About That Sponge!


The purpose of this article is to discuss kitchen sponge cleanliness, along with how often and how to clean your kitchen sponge. Kitchen sponges can be one of the dirtiest items in your house or apartment. Studies have found that kitchen sponges can have millions of bacteria, including coliform bacteria, which show that the sponge is dirty from fecal matter. After two weeks of use, a sponge can have around 8 million bacteria. That’s a lot of germs. To keep your sponge clean and prevent spreading bacteria, clean it at least once a week. Here are some good ways to clean a sponge: Microwave the wet sponge on high for 1 minute (but only if the sponge doesn’t have any metal in it); soak the sponge in 10% bleach for 1 minute; soak it in 70% ethanol for 1 minute; or run the sponge through the dishwasher (1 complete cycle) on the hot cycle. Sponges can be very helpful for cleaning, but they can be a place where many germs grow. Therefore, it is very important to clean your sponge often to stop the spread of bacteria.


Have you ever had food poisoning? Vomiting, nausea, stomach cramps, diarrhea, fever, and headaches are not something anyone wants to go through. Food poisoning, also called foodborne illness, happens when we eat things that contain certain bacteria, viruses or parasites in them (CDC, 2024). One out of every six people in the United States will get food poisoning each year (CDC, 2018). Most of the time, the symptoms go away in a few days (1-7 days), but sometimes the bacteria can cause long-term health problems, like irritable bowel syndrome (IBS), kidney issues, arthritis and other autoimmune problems. Luckily, these long-term problems from food poisoning only happen in about 2-3% of food poisoning cases (Lindsay, 1997).

About 12% of foodborne illnesses come from home cooked meals. However, this number is probably even higher than that. Many people don’t report when they get sick because they aren’t sure if it’s from the food they ate or just the flu (Dewey-Mattia, 2018). One way to get food poisoning is from food that touches a dirty surface before you eat it. This is known as cross-contamination because the food picks up the “dirt” or germs (bacteria, virus or parasite) from the other ‘soiled’ surface. Cross-contamination can happen from anything in your kitchen that is not clean, like your hands, the countertop, cutting boards, knives, and other unclean or uncooked food. Sometimes, we may think that we have cleaned a surface, but it may not actually be clean. That’s because we can’t see bacteria without a microscope. The “tools” or items that we use to clean the kitchen are just as important as washing and cleaning the food we eat. Many of us think our brushes, sponges and dishcloths are clean because we use them with soap and water or a sanitizer; however, these items can be some of the dirtiest things in our kitchen, and they can cause us to accidentally contaminate our food. That’s because common dishwashing soaps often don’t reduce the number of microbes on sponges and dishcloths that are heavily soiled (Sharma et al., 2009). However, there are other ways to clean your sponge that we will discuss in this article.

Kitchen Sponges

Who doesn’t love a nice kitchen sponge? They seem like the perfect cleaning tool, but did you know that sponges can actually pick up and hold onto bacteria for a long time? Typical household sponges are made from wood pulp, which is called cellulose (Figure 1). Cellulose sponges are an environmentally friendly product because they can break down easily in a landfill when you throw them away. As consumers, a sponge is often our “go-to” cleaning tool because it is convenient and good at wiping up spills, washing surfaces, or cleaning dishes. However, some of the same characteristics that make a sponge a great cleaning tool also make it the perfect place for bacteria to hide and grow. We did a study on cleanliness by testing 14 different apartments where college students live. We compared our findings to what other researchers reported, and everyone agrees that the kitchen sponge is one of the dirtiest, if not the dirtiest, item in the house.

Environmentally friendly cellulose sponges have different sized pores that make it easy for food and bacteria to become trapped inside.

Environmentally friendly cellulose sponges have different sized pores that make it easy for food and bacteria to become trapped inside.
Dr. Julie Northcutt ©2024, Clemson University.

Figure 1: Two different types of commercially available cellulose sponges with a scrubbing feature on one side.

Is My Kitchen Sponge Really the Dirtiest Item in My Kitchen?

The simple answer to this question is YES; it probably is the dirtiest item in your kitchen, and maybe even in your house. Kitchen sponges are the perfect place for bacteria to live and grow. This is because the sponges have tiny holes that hold water, food bits and food juices that are needed for bacteria to survive. One researcher described the kitchen sponge as “tiny rooms within rooms,” where there are plenty of extra places (surfaces) for bacteria to attach (Dr. Lingchong You, Duke University). This makes the sponges the perfect “apartment complex” for bacteria, where they have their own free delivery of food and water from the spills we wipe up.

When we use a dirty sponge with our bare hands, the sponge can transfer bacteria (cross-contaminate) to our hands. Then, we can transfer the bacteria on our hands from the sponge to the food we are eating or handling. When we use a dirty sponge to wipe a surface, we could be spreading bacteria all over that surface instead of cleaning it. A study by the National Science Foundation looked at household items from 22 families over a one-month period (NSF, 2011). They found that 75% of the household sponges and dishcloths had Coliform bacteria (think E. coli, which is a type of coliform bacteria). Coliform bacteria usually indicate that there is a fecal contamination. The study also found that more bacteria transferred when the “dirty” sponge was used with more force (scrubbing harder freed more bacteria from the sponge to transfer to the other surface). Another study found that the average number of bacteria in kitchen sponges was nearly 32 million, but this study only tested a few sponges (Knoll, 2019).

In our study of college student apartments, we tested the number of bacteria or yeast and mold in 14 different apartments over six weeks and found the following:

  • Kitchen sponges had over 7.9 million bacteria per sponge (that is more than 7,900,000).
  • Kitchen sink had nearly 32,000 bacteria/25 cm2 (25 cm2 is the same size as a sponge)
  • Kitchen counters and toilet seats had similar amounts of bacteria (316 and 398 bacteria/ 25 cm2).
  • Refrigerator door handles had about 100 bacteria/25 cm2.

We also tested kitchen sponges used by college students for three weeks. After one week, the sponges had nearly 400,000 bacteria per sponge. This increased to 20 million bacteria/sponge by weeks 2 and 3.

Cleaning Kitchen Sponges

Our study shows that if you use a kitchen sponge, you should clean it at least once each week. When the kitchen sponge becomes worn (torn or discolored), you should replace it with a new one sponge. A worn or torn sponge provides more places for bacteria to hide.

How Do I Clean My Sponge:

Here are some good ways to clean a traditional cellulose sponge: (these are not in any order, but all work)

  • Microwave a wet sponge on high for 1 min (but only do this for sponges that DO NOT CONTAIN ANY METAL pieces in them. Metal is sometimes for scrubbing, but you should not microwave metal).
  • Soak the sponge in 10% bleach (the over-the-counter kind from grocery) for 1 min.
  • Soak the sponge in 70% ethanol (this is not the same as rubbing alcohol, and it’s the kind of ethanol you can drink)
  • Run it through one complete cycle in dishwasher on high heat.

If none of these methods seems appealing to you, you can always just replace your sponge with a new one.

Cleaning or replacing your kitchen sponge regularly will help prevent the spread of bacteria and keep your kitchen cleaner and safer.


  1. Centers for Disease Control and Prevention (CDC). 2024. Symptoms of food poisoning.

Access date June 24, 2024.

  1. Centers for Disease Control and Prevention (CDC). 2018. Burden of foodborne illness: Findings. Access date June 24, 2024.
  2. Dewey-Mattia D. 2018. Surveillance for Foodborne Disease Outbreaks—United States, 2009–2015. MMWR Surveill. Summ. 67:1–11. doi: 10.15585/mmwr.ss6710a1.
  3. Knoll, S. (2019). The Microbial Community of Kitchen Sponges: Experimental Study Investigating Bacterial Number, Resistance and Transfer. Honors Theses.
  4. Lindsay, J. 1997. Chronic sequela of foodborne disease. Emerging Infectious Disease 3(4): 443-452.
  5. NSF. (2011). 2011 NSF International Household Germ Study. Retrieved from
  6. Sharma M, Eastridge J, Mudd C, 2009. Effective household disinfection methods of kitchen sponges. Food Control 20:310-3.

Originally published 07/24

If this document didn’t answer your questions, please contact HGIC at or 1-888-656-9988.

Factsheet Number



Pin It on Pinterest

Share This