Is the 5-Second Rule Real?

In Too Afraid to Ask, we’re answering all the food-related questions you’d rather not have loitering in the search history of your corporate laptop. Today: Is the five-second rule actually real?

My curse is clumsiness. Forever, I’ve sent any edible object in my radius flying like a frisbee at the park. Grape soda ended up all over my brother’s electric keyboard in high school. I once woke up after a big night on the sauce in London with pieces of jam toast smooshed into my bedroom carpet. And I’m not sure I’ve ever crushed garlic without a clove launching itself off the cutting board: “Five-second rule!” I’d holler each time, swooping down to recover my rogue spoils.

But is the five-second rule even real? I hadn’t questioned it until a colleague shared a tweet from public health scientist and epidemiologist Eric Feigl-Ding, Ph.D., debunking the theory. “​​The ‘5 second rule’ for dropped food [is] not a safe thing,” he wrote. “Microorganisms that cause certain diseases can transfer to food immediately.” I felt mortified—had my coworker caught me eating salt and vinegar chips off the gray carpet under my desk?—and betrayed by folk science.

The rule’s “genesis is difficult to ascertain,” says Paul Dawson, Ph.D., a food scientist at Clemson University. In Did You Just Eat That, Dawson and his co-author, Brian Sheldon, Ph.D., wrote that an early iteration is sometimes attributed to Mongol ruler Genghis Khan. During his 13th-century reign, food that fell on the floor at one of the Khan’s elaborate banquets could stay there as long as he deemed fit; the delicacies were simply too good to ever go bad. Fast forward to the 1960s, when Julia Child echoed the same sentiment on her cooking show, The French Chef. After dropping a potato pancake on the stovetop, she wasn’t phased: “But you can always pick it up, and if you are alone in the kitchen, who is going to see?” Child told her audience.

These days, scientists know a whole lot more about what might be lurking on our floors. Viruses, microorganisms, bacteria, and foodborne pathogens, like E. coli and Salmonella, can all be found on everyday surfaces, says Donald Schaffner, Ph.D., a food science professor at Rutgers University. Some likely come from the air, while others are transmitted from surface-to-surface contact—via shoes, kids, or pets. Most of these won’t make us sick, he says, but some can: “If a foodborne pathogen from the floor were to be eaten, symptoms could include nausea, vomiting, and diarrhea.”

There’s no amount of time that would guarantee none of those bacteria or pathogens transfer from floor to food, says Schaffner. In a 2016 study, he found that the longer the test foods—watermelon, bread, buttered bread, and gummy candy—sat on the inoculated surfaces, the more bacteria they would pick up. But the amount of moisture in the food was a bigger factor in determining how intensely and how quickly cross-contamination occurred. When testing wetter foods like watermelon, “we almost always saw 100% of the bacteria transfer virtually instantaneously,” says Schaffner.