The five-second rule in food has always been a somewhat dubious idea that people have enthusiastically embraced anyway: any food dropped on the floor is still safe to eat if you pick it up in less than five seconds. Now, scientists have proven that this is, indeed, a myth.
Researchers from Rutgers University in New Jersey report that bacteria from any surface can transfer onto food very quickly, in less than a second even. Donald Schaffner, a co-author on the study and a microbiologist, says,
The 5-second rule is a significant oversimplification of what actually happens when bacteria transfer from a surface to food.
To prove the point, the researchers coated four different surfaces with bacteria – stainless steel, wood, carpet and ceramic tile. Then they dropped various kinds of food on the surfaces, allowing them to sit for less than a second, five seconds, 30 seconds and five minutes. They used bread and butter, watermelon, bread, and gummy candy.
The results of the experiments showed that the longer food was left on the contaminated surfaces, the more bacteria swarmed onto it. And some took less than a second.
Watermelon gathered the most bacteria, and gummy candy picked up the least. Researchers say this was most likely due to the high moisture content in watermelon.
Schaffner explains, “Bacteria don’t have legs. They move with the moisture, and the wetter the food, the higher the risk of transfer.” Carpet had the lowest bacteria transfer rate compared to the other surfaces, the study notes.
There are other factors that affect how much bacteria can collect on a piece of food than the amount of time it sits on a surface, the study shows. These include the kind of food, the type of surface involved, and the type of bacteria present.
The study was published in the journal Applied and Environmental Microbiology.
An earlier study also tested the five-second rule in 2014 and found that the amount of time food sits on a surface can affect the amount of bacteria that transfers onto it, with contrasting results that proved the five-second rule true, Live Science reports. However, this study was not published in any peer-reviewed journals.