Down and out: Why the five-second rule isn’t safe

November 9, 2018

How does eating something that you just dropped on the floor compare to leaving your seatbelt unlatched when you are in the car? It may be okay this time—but you are taking a huge risk, according to a report by Prevention magazine posted on November 8.

This may or may not surprise you, but what is widely known as the “five-second rule” is an old wives’ tale, food scientists (and authors of Did You Just Eat That?)  Paul Dawson and Brian Sheldon have determined. “There is conclusive evidence that when food comes into contact with a contaminated surface, bacteria are transferred immediately,” they warn.

In 2006, Dawson and his colleagues in the Department of Food Science and Human Nutrition at Clemson University in South Carolina published the first peer-reviewed study on the five-second rule. The researchers tested the rule by contaminating three different surfaces—tile, carpet, and wood—with salmonella, dropping food (specifically, bologna and bread) on each surface, and measuring how much bacteria was picked up by the food within five, 30, or 60 seconds.

“Our findings pretty conclusively busted the myth of the five-second rule,” they wrote. “We found that bacteria transferred to the bologna after only five seconds of contact time….” And the more time the food spends on the floor, the more bacteria it attracts.

Even worse, according to Prevention, Dawson’s experiment also found that salmonella hung around on the contaminated tile surface for a month. “Bacteria capable of forming spores are known to survive for years in their dormant spore form,” the authors said.

FYI, this isn’t the only research to debunk the five-second rule, Prevention found. In 2016, a second peer-reviewed study conducted by Rutgers University in New Jersey reported similar findings; although the researchers included a wider variety of food in their experiment—watermelon cubes, plain bread, buttered bread, and gummy bears—on a variety of surfaces. (Because bacteria move quickly through moisture, the watermelon sucked up the greatest number of germs.).

The bottom line: The five-second rule is a gross simplification of how bacteria transfer to food, and there are many more factors than simply how long food sits on a surface—for example, the type of food, whether it’s carpet or tile, and how contaminated that surface is. So don’t take any chances. Discard that tasty morsel.

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