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Scientists say drop 'five-second rule' for food on floor

Depending on the surface, food and time it sits on the floor, bacteria can transfer in less than one second, researchers say.

By
Stephen Feller
Although the five-second rule is often applied to all types of food, researchers found the wetness of foods and flatness of a floor affect how bacteria can transfer from one to the other -- and it can happen in as little as one second, proving the rule incorrect. Photo by Monkey Business Images/Shutterstock
Although the five-second rule is often applied to all types of food, researchers found the wetness of foods and flatness of a floor affect how bacteria can transfer from one to the other -- and it can happen in as little as one second, proving the rule incorrect. Photo by Monkey Business Images/Shutterstock

NEW BRUNSWICK, N.J., Sept. 14 (UPI) -- The five-second rule is ubiquitous: Adults and children, slovenly and squeaky-clean people alike, often scoop food off the floor after it drops and, as long as it has been less than five seconds, eat it without second thought.

The problem is, the rule is not rooted in reality.

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Depending on the food and the surface it falls on, bacteria can contaminate food in anywhere from one to 300 seconds, rendering the five-second rule as occasionally true but mostly myth, according to a new study published in the journal Applied and Environmental Microbiology.

The five-second rule posits that as long as food has been on the floor for less than five seconds, it should be safe to eat because it takes time for bacteria to transfer. Not everyone believes the rule but for many it justifies salvaging lost food.

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Researchers at Rutgers University acknowledge research into the five-second rule is light and inconsequential, but the results of their study suggest a lot of people are exposing themselves to potential pathogens because they have no idea how bacteria move and how long it takes.

For the study, researchers tested the time to contamination for watermelon, bread and butter, plain bread and gummy candy when they fall on stainless steel, ceramic tile, wood or carpet. Each food was dropped on each surface, after being contaminated with bacteria, for less than one second, five seconds, 30 seconds and 300 seconds.

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After repeating each combination of food, surface and exposure time 20 times each -- for 2,560 measurements of time to contamination -- the researchers found wetness of food and topography of surface play a significant role in how quickly bacteria can transfer from the floor to food, with time of exposure often being meaningless.

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Watermelon picked up the most contamination on all surfaces, because the more wet a food is, the easier it is for bacteria to exist on it. Surfaces that are more flat, such as tile and stainless steel, also had much higher rates of bacterial transfer than carpet or even wood, which has a variable surface.

"The five-second rule is a significant oversimplification of what actually happens when bacteria transfer from a surface to food," Donald Schaffner, a professor and extension specialist in food science at Rutgers, said in a press release. "Bacteria can contaminate instantaneously."

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