Are the Germs in Your House Making You Sick?

Research tells us the most likely places to find germs in the house.

Posted Sep 06, 2019

ridvanarda/Adobe Stock
Source: ridvanarda/Adobe Stock

Germs surround us everywhere; that’s a fact of life. But there are some places—even in your own home—that are breeding grounds for bacteria. Let’s take a careful look at what the evidence says about where the germs live in your house.

First, can you guess the worst offender for breeding germs? It’s not the toilet seat or even the floor—it’s your kitchen sponge. A study published in Nature’s Scientific Reports investigated which and how many bacteria typically live in a kitchen sponge, and the best way to clean them.

The study found that as many as 362 different species of bacteria live inside an average kitchen sponge, and there are a lot of them—about 82 billion in a cubic inch of space. In case you’re counting, that’s about the same number of bacteria found in a human stool sample. Many of these bacteria are harmless to people with normal immune systems. But if you’ve used your sponge to wipe up a drip of raw egg or some dirt from fruit and vegetables, it can harbor bacteria that will make you sick.

Using a sponge to wipe down kitchen surfaces just spreads these bacteria—to the inside of your microwave, your refrigerator’s handle, or your kitchen counter.

Furthermore, the study found that trying to clean a sponge can actually lead to more bacteria. That’s because a typical cleaning job—whether microwaving the sponge, dousing it in a cleaner, or running it through the laundry—gets rid of the weaker bacteria, leading more space for the stronger bacteria to reproduce.

Your best bet? Throw out your kitchen sponge every week and start with a new one.

Now that we’ve tackled the germy-kitchen sponge, let’s move onto your kitchen floor. You’ve undoubtedly heard of the five-second rule, which means if you pick up dropped food within five seconds of it hitting the floor, it’s still okay to eat.

A microbiologist at Rutgers University led a study to find out if this rule is scientifically sound. His study team tested four different foods—watermelon, bread, buttered bread and gummy candy—on four different surfaces—stainless steel, ceramic tile, wood and carpet—for four lengths of time—less than one second, five seconds, 30 seconds and five minutes.

They found that food that touched the ground for any length of time—even less than one second—was contaminated. And the longer a piece of food stayed on the ground, the more bacteria it picked up.

Watermelon picked up the most bacteria—most likely because it is wet—and gummy candy picked up the least. Carpet was the least likely surface to transmit bacteria, while steel and ceramic were the most likely.

Again, many of these bacteria are harmless to people; and exposure to germs can even help to bolster your immune system, reducing the chance you’ll get sick later. But germs that make you sick, such as the viruses that cause colds and the flu, can survive on surfaces for days. The bottom line: The five-second rule doesn’t hold up; if you drop food on the floor, it’s best to throw it out.

Finally, what about wearing shoes in the house? A study conducted by a microbiologist at the University of Arizona studied how much and which types of bacteria remained on shoes throughout the day. He found that shoes do pick up and track bacteria over long distances, but less than you might think. Compare shoes to your kitchen sponge: studies found 421,000 units of bacteria on the outside of a shoe versus 82 billion in a cubic inch of a sponge.

While that’s still enough bacteria to warrant not eating off the floor (see the five-second rule above), wearing shoes in the house is not the biggest source of germs in most homes. Of course, there are exceptions. If you have been mucking horse stalls, for example, it’s probably best to take your shoes off at the door. If you have a crawling baby in your home, it’s also a good idea to take off your shoes in the house. And if you suffer from environmental allergies, taking off your shoes can reduce the number of allergens in your home. Overall, if you want to focus on reducing how many germs you are exposed to in your house, replace that kitchen sponge and don’t eat food that’s dropped on the floor.