You or someone you know has probably made the claim that it's OK to eat food that falls on the ground if it's picked up in less than five seconds. That chocolate chip cookie that slipped out of your hand? Totally cool to eat off the ground because it was just there for three seconds. That last bite of sandwich? It was only on the ground for two!
Is that how the transfer of bacteria actually works? As it turns out, the answer is a little more complicated than you might think.
On a recent episode of Slate's podcast, The Gist, Mike Pesca and New Yorker writer Maria Konnikova dig a little deeper into the science behind the five-second rule. In the episode, Konnikova cites a study by Paul Dawson from Clemson University, who dropped baloney on different floors – tile, wood, and carpet – to see how fast bacteria attached to the food.
In order to see how much bacteria was on the floor, Dawson and his students first looked at what bacteria was actually on the surface. After five seconds of being on a tile floor, they found that the baloney had picked up 99% of that bacteria. In fact, this bacteria transfer proved to be almost immediate when the baloney touched the floor.
So no, the five-second rule is not real.
What was interesting from their findings, however, is that the bacteria transfer varied from surface to surface. While the baloney that fell on the tile floor had 99% of the original bacteria on the floor after five seconds, it was less for wood floors, and even less for carpet. The floor type matters! Maybe we should all add carpet to our kitchens.
But to be totally honest, regardless of this surprising difference in bacteria with floors, you probably should just avoid eating food off the ground all together. Do you even want to know how long E. coli lasts on the floor? You really don't.
→ Listen: Is The "5-Second Rule" Baloney? from Slate's The Gist