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Rethinking The Five-Second Rule: With Carpet, There's No Rush

Bacteria don't wear wristwatches. But they can take their sweet time hopping onto a potato chip.
Greg Williams/Wikimedia Commons
Bacteria don't wear wristwatches. But they can take their sweet time hopping onto a potato chip.

Many of us will happily eat a gummy bear or cookie after it falls on the floor, as long as we snatch it up quickly. Say, five seconds or less, right?

Well, science just gave us another excuse to continue this food-saving habit, especially when it comes to carpet-dusted snacks.

Biology students at the Aston University in Birmingham, U.K., measured how quickly two common bacteria hop aboard foods dropped on tiles, linoleum and carpet.

Their findings support the idea that there really is such a thing as the five-second rule for moist snacks, such as wet pasta and sticky gummy bears.

For dry foods, like cookies and toast, waiting a full 30 seconds didn't make much of a difference in the number of critters that jumped on, microbiologist Anthony Hilton and his students reported this week on the university's website.

The team hasn't published the data yet. So the findings are still preliminary and need to be confirmed.

But the conclusions make sense: If you snatch up a wet gummy bear three seconds after it hits a tile or laminate floor, it will pick up much fewer microbes than if you wait 30 seconds — at least for the two bacteria examined, E. coli and Staphylococcus aureus.

And for carpet, you've got an even longer grace period. It didn't matter whether the food was wet or dry, the surface spread the least germs, even over the full 30 seconds, the team found.

"We have found evidence that transfer from indoor flooring surfaces is incredibly poor, with carpet actually posing the lowest risk of bacterial transfer onto dropped food," Hilton saidin a statement.

With carpet, of course, your sticky candy will pick up much more than bacteria, especially when you have furry family members.

But that doesn't seem to deter many folks from sampling off the floor. Hilton and his students surveyed about 500 people and found that 87 percent of them said they eat dropped snacks. And about three-quarters of these people use the five-second rule.

Not everyone agrees that this is such a good idea.

The guys over at Smithsonian.com recently reminded us that whether or not you get sick from floor-tainted food depends on which particular critters are hanging out on your linoleum — and not necessarily on the total amount of microbes.

"Eating food off the floor is a bit like playing Russian roulette with your gut," molecular biologist Eric Schulze says in a video on Smithsonian's website. "We track harmful agents like fecal bacteria on the soles of our shoes all the time. So no floor surface is guaranteed to be a safe bet," he adds.

Although Hilton and his team didn't find any fecal bacteria on the indoor floors they examined, it only takes a few of the wrong microbes to make you really sick.

So the conclusion? Sampling food from the floor comes with a risk, especially if you don't know how clean that tile is. But grabbing it quickly could make a difference for sticky snacks.

Copyright 2021 NPR. To see more, visit https://www.npr.org.

Michaeleen Doucleff, PhD, is a correspondent for NPR's Science Desk. For nearly a decade, she has been reporting for the radio and the web for NPR's global health outlet, Goats and Soda. Doucleff focuses on disease outbreaks, cross-cultural parenting, and women and children's health.