The next time you're side-eyed or shamed for eating food dropped on the floor, know that you're not alone. Seventy-nine percent of people have admitted to eating food off the floor, and now the science of the "five-second rule" backs you up. Yes, really.
According to Aston University microbiologist Anthony Hilton, food is usually safe to consume after it's been in contact with the floor for a few seconds. Let me explain.
The five-second rule is a highly contested concept: some argue that people have up to a five-second window to pick up and consume fallen food without severe consequences, while others maintain contamination happens immediately. It is difficult to pinpoint where the rule got its start, but has been traced back to Genghis Khan — although this is neither official nor verified.
"Obviously, food covered in visible dirt shouldn't be eaten, but as long as it's not obviously contaminated, the science shows that food is unlikely to have picked up harmful bacteria from a few seconds spent on an indoor floor," the germ expert says, reports The Independent.
Hilton says there are variables to keep in mind, like what type of food and how dirty the surface. Some foods, say ice cream or jam, are more likely to pick up dirt than others. Type of surface also plays a role, as Hilton says a tile-like surface is worse than carpet. Generally speaking, so long as the surface is clean to the naked eye, it should be okay to eat.
There Is Still Bacteria — Don't Get Too Excited
It is important to note that this does not mean bacteria won't be transferred in five seconds. A two-year study from Rutgers University food microbiologist Donald W. Schaffner found that food picks up bacteria no matter how quickly you pick it up from a surface. "Bacteria can contaminate instantaneously," Schaffner says in a news release.
In Schaffner's study, four different foods (cut watermelon, bread, buttered bread, and strawberry gummy candy) were tested on four different surfaces (stainless steel, ceramic tile, wood, and carpet) for four different contact times (less than one second, five seconds, 30 seconds, and 300 seconds). The study found that longer contact times results in greater contamination; carpet had a low rate of transmission and moist foods (like watermelon) had highest rates of transmission.
But Hilton isn't denying that germs aren't transferring when food comes into contact with the floor. He's just making the point that depending on the item, the surface, and the condition of the floor, it can be relatively okay to quickly pick up and consume a food.
"That is not to say that germs can't transfer from the floor to the food," says Hilton. "Our research has shown that the nature of the floor surface, the type of food dropped on the floor, and the length of time it spends on the floor can all have an impact on the number that can transfer."