For Disinfecting Sponges, Microwaving is a Simple Solution

Ah, the lowly kitchen sponge.  It is the seemingly perfect scrubbing tool that can take repeated use and abuse as it helps you scrub the dishes, wipe up food debris and even clean the kitchen sink.  However, as we all know, you don’t get something for nothing in this world!  From a microbiological point of view, the sponge may be the most contaminated item in your home (University of Arizona Information for News Media).   And how do you clean the sponge that just contacted foods such as raw egg, uncooked meat or raw vegetables?  Run it under water, adding some soap for good measure then squeezing a couple times? Toss it in the dishwasher or washing machine?  A team of researchers from the University of Florida found that another kitchen mainstay, the microwave oven, may offer the simplest effective option for disinfecting sponges (journal abstract).

A Mobile Home for Germs

After a short period of normal use, invisible microbes take up residence in sponges.  Coliform bacteria (the type of bacteria likely to be in poop, sorry) begin to thrive in the many nooks and crannies of damp sponges, supported by moisture and nutrients in food debris; viruses may find a comfy place to hang out.  In a process known as cross-contamination, germs may hitch a ride on the kitchen sponge from one surface to another as the kitchen gets a wipe-down.  All of this activity has the potential to expose your family to disease-causing germs, such as norovirus (aka “the stomach bug”), E. coli and Salmonella.  Microbiologist Dr. Chuck Gerba made the interesting observation in a 2004 New York Times interview that some of the cleanest-looking kitchens often have bacteria all over the kitchen because “clean” people wipe up so frequently.  Amusingly, some of the cleanest kitchens, Gerba jokes, are in the homes of bachelors who rarely wipe up countertops.

Most of us would like to be able to use and reuse sponges without dreading the consequences of spreading germs. The University of Florida team reported simply microwaving sponges (wet, never dry) for two minutes at high power killed or inactivated over 99 percent of all the living pathogens in sponges and cleaning pads that had been soaked in a “witch’s brew” of fecal bacteria, viruses, protozoan parasites and bacterial spores (University of Florida News). The researchers recommend “zapping” kitchen sponges every other day or so. This is a simple and effective method when carried out properly (with the emphasis on “properly” because improper microwaving of sponges can cause severe skin burns and has the potential to start a fire).

Microwave Sponges Safely

The research team emphasizes three points of precaution when microwaving sponges:

  • To guard against the risk of fire: Ensure sponge is completely wet before placing in the microwave oven.
  • To guard against burns: Be careful when removing sponge from the microwave oven as it will be hot and there may be steam when the microwave is opened.
  • To guard against electrical shorting: Sponges should have no metallic content.

According to the Centers for Disease Control and Prevention, each year one in six Americans (48 million) gets sick, 128,000 are hospitalized, and 3,000 die of foodborne illness.  Properly microwaving sponges on a regular basis is one step that could go a long way to help keep your family healthy and prevent costly medical visits.

Barbara M. Soule, R.N. MPA, CIC, is an Infection Preventionist and a member of the Water Quality & Health Council.

1High power may vary among microwave ovens, but this point is not addressed by the researchers. The researchers used a Sharp, Model R-630D microwave oven with a rotating glass plate, a frequency of 2,459 MHz, and power of 1,100 watts.