Debunker: The “5-Second Rule”
It’s time for a snack, and you’re holding a piece of buttered toast. Then—damn it!—you drop it. Of course it lands butter side down. You don’t want to go through the rigmarole of toasting and buttering another, so you pick it up, quick as a flash, reasoning to yourself that those three or four seconds on the floor likely haven’t made much difference one way or the other.
The popular myth that food is fine to eat from the floor, so long as you pick it up in five seconds or less—known as the “five-second rule”—has sometimes been traced back to footage of the American chef and food writer Julia Child. “You must have the courage of your convictions,” she says, before flipping part of her potato pancake out of the pan and onto the stovetop. As she pushes the mixture back into the pan with her fingers, she adds, wryly: “But you can always pick it up, and if you are alone in the kitchen, who is going to see?”
Julia Child was a wonderful chef, but she was not a food-safety expert. In one of few peer-reviewed studies testing the five-second rule, scientists from Rutgers University in 2016 actually found that it doesn’t really matter whether you leave food on the floor for three seconds or 300 before you eat it. The greatest jump in the number of bacteria on your food occurs in the first couple of seconds. “Some [bacteria] transfer takes place ‘instantaneously,’ at times of less than one second, disproving the five-second rule,” write authors Robyn C. Miranda and Donald W. Schaffner.
So what does this mean for hungry folks trying to decide whether a bit of floor seasoning means their toast is a write-off?
The amount of time your breakfast has contact with the floor is seemingly less important than the surface you drop it onto. While intuitively you might assume that clean smooth tile would have the least effect on food, the evidence suggests otherwise: “Carpet has very low transfer rates,” write Miranda and Schaffner, “compared with those of tile and stainless steel, whereas transfer from wood is more variable.” The relative moisture of the food also seems to make a difference: More moist food, like watermelon, drew the highest rate of contamination, while less moist food, like a gummy candy, drew the least.
That doesn’t mean all dropped food should necessarily go straight in the trash, though. In the vast majority of cases, the study’s authors write, eating food that’s spent a few seconds on your clean kitchen floor is unlikely to make you sick. After all, we put food down on less-than-pristine surfaces all the time: The average desk—which you’ve no doubt rested a sandwich or two on, with no ill effects—has 400 times more germs on its surface than a toilet seat, according to one study. There’s even evidence that suggests that an overuse of antibiotics, household disinfectants, and other sanitizing products may have a negative effect on our microbiome and the “good bacteria” that help our bodies fend off disease. Is a little floor toast from time to time such a bad thing?
That said, you don’t want to court disaster, either. From a food-safety perspective, E. coli and salmonella are two particularly worrying sorts of bacteria that you really don’t want to get on your food. E. coli can be especially virulent, with as few as 10 cells of some strains causing severe illness or even death in people with compromised immune systems. And though both are rare, they together cause hundreds of deaths and hundreds of thousands of infections in the United States each year. These bacteria are much less likely to be on your floor—or desk—than in undercooked chicken or a bag of unwashed lettuce.
So don’t worry too much about how many seconds your food is spending on the floor, and focus your attention instead on more valuable questions of food safety, including being particularly careful around raw meat, washing your hands, knives, and cutting board regularly, and avoiding unpasteurized milk. And if you are going to eat toast off the floor, just make sure it’s clean—and pick off the carpet fluff first.