You can't see them, but your house is teeming with germs.
Many of these germs aren't harmful. In fact, most of them come from your own body, and some can even be beneficial.
But sometimes nasty pathogens can creep in from the outside and make you very sick.
So what is the biggest source of harmful germs in your home?
Your kitchen sponge, Philip Tierno, a microbiologist and pathologist at the New York University School of Medicine, told Tech Insider.
That's right. Not your toilet bowl. Not your trashcan. Rather, the object many of us wash our dishes with every single day.
"That thing is very dirty," Tierno said. "Mainly because you're cleaning up vegetables, carcasses of meat, and all sorts of food stuff that can potentially contain pathogenic [disease-causing] bacteria that will grow in numbers over time."
Sponges are ideal breeding grounds for microbes because we supply them with a nourishing, warm, moist environment - and tons of food.
"The moisture assures the good growth, but you also have the nutritive material that you're taking in," Tierno said.
Sponges can carry all kinds of nasty bacteria, including campylobacter, salmonella, staphylococcus, E. coli, and listeria - all of which can cause mild to severe gut and skin infections.
Campylobacter bacteria, which is commonly found in food such as raw chicken, is by far the biggest contributor to foodborne illness in the US. It affects more than 1.3 million people here every year.
Within two to five days after exposure, campylobacter can ravage the digestive tract, causing diarrhea, cramping, abdominal pain, fever, nausea, and vomiting. It can even cause a life-threatening blood infection in those with compromised immune systems.
Vegetables may also transfer nasty bugs onto a sponge. This includes E. coli, which can cause diarrhea, urinary tract infections, pneumonia, and other illnesses.
"Even if you rinse it and use some soap, it's not sufficient to eradicate the germs," Tierno said.
So how can you ensure that your sponge doesn't cause your next big bout of food poisoning?
Forget the microwave. "The best way is to put it in a little bleach solution," Tierno said. Every time he preps food, he puts a jigger of bleach into a half quart or quart of water, then rinses the sponge with it to prevent cross contamination.
"It's very potent. It can kill anthrax spores," Tierno said.
About 56,000 people are sickened by foodborne illness each year in the US. And believe it or not, the primary source of this illness comes from the home.
So next time you're cleaning up after your chicken dinner, throw that sponge into a pool of bleach water. Your intestines will thank you.