Study: Five-Second Rule Is (Mostly) Legit

Your News Companion by Ben Mathis-Lilley
March 15 2014 4:18 PM

Study: Five-Second Rule Is (Mostly) Legit

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"The findings of this study will bring some light relief to those who have been employing the five-second rule for years," says Aston University's Anthony Hilton

Photo by MARK RALSTON/AFP/Getty Images

A UK study is contradicting the conventional wisdom that the five-second rule is mostly bunk, claiming the amount of time food is on the ground really does have an effect on how much bacteria gets on the dropped item. Especially when it comes to carpeted floors, five seconds isn’t even cutting it close, according to a group of biology students at Aston University in Birmingham. As part of the study, the students measured how long it takes two common bacteria to attach to dropped food and concluded there really is such a thing as a five-second rule. And for dry foods, like a cookie, there may even be a 30-second rule.

According to the preliminary findings of the unpublished study:

Time is a significant factor in the transfer of bacteria from a floor surface to a piece of food; and
The type of flooring the food has been dropped on has an effect, with bacteria least likely to transfer from carpeted surfaces and most likely to transfer from laminate or tiled surfaces to moist foods making contact for more than 5 seconds.
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The findings appear to contradict a much-discussed 2007 study from Clemson University that argues there is no time period in which eating food that has been dropped on the floor is OK. Aston University’s Anthony Hilton says his students’ findings supported the previous study that bacteria gets transferred to the food immediately. But “ the transfer efficacy is extremely low … hence the five-second rule,” according to National Geographic. Hilton warns that
"consuming food dropped on the floor still carries an infection risk as it very much depends on which bacteria are present on the floor at the time." And that's partly the reason why, in a video on the Smithsonian’s website, Eric Schulze compares adhering to the five-second rule to “playing Russian roulette with your gut.”   

Regardless of whether it’s scientifically proven, the truth is most people adhere to the five-second rule. In a survey carried out by the Aston University team, almost 90 percent of people acknowledged they would eat, or have eaten, food that was dropped on the floor.

Daniel Politi has been contributing to Slate since 2004 and wrote the "Today's Papers" column from 2006 to 2009. You can follow him on Twitter @dpoliti.

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