The five-second rule is, without a doubt, one of the world's most enduring myths.
And many of us swear by the idea that, if you drop something scrummy on the floor, there’s a five-second window of grace in which you can pick it up, dust it off, and gobble it down – all without falling foul of floor germs.
Donald Schaffner, professor and extension specialist in food science, said: "the popular notion of the 'five-second rule' is that food dropped on the floor, but picked up quickly, is safe to eat because bacteria need time to transfer.
“We decided to look into this because the practice is so widespread. The topic might appear 'light' but we wanted our results backed by solid science.”
They aren’t kidding; the five-second rule is so ingrained in popular culture that it’s even featured in two television shows.
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However, as it turns out, five seconds isn’t fast enough.
“The five-second rule is a significant oversimplification of what actually happens when bacteria transfer from a surface to food,” said Schaffner. “Bacteria can contaminate instantaneously.”
That’s right; no matter how quick you are, you’re very unlikely to snatch dropped goodies up quickly enough to stop bacteria infecting them.
It actually takes less than a second for food to become contaminated after hitting the floor.
If you will persist on eating from the floor, however, it’s worth remembering that some surfaces are safer to eat off of than others – and some types of food, too.
More moist foods, such as watermelon, are best thrown out after hitting the ground. Dryer foods, such as gummy sweets, have a lower risk of bacterial transfer.
Unexpectedly, carpet is by far the safest surface to eat dropped food off of – while tiles and stainless steel floors are more likely to spread bacteria from one surface to another.
"Bacteria don't have legs, they move with the moisture, and the wetter the food, the higher the risk of transfer,” explained Schaffner.
He added: “Also, longer food contact times usually result in the transfer of more bacteria from each surface to food.”
So, on reflection, it’s probably best if you only pick up that bagel to drop it into a nearby bin.