April 24, 2019

The Five-Second Rule: Folk Wisdom or Scientific Fact?

Written by Garret Weigel | Food Safety

“Oh no, I dropped my french fries! Hey, no problem, five second-rule!”


Even if you’ve never followed this bit of popular folk wisdom yourself, you’ve probably heard it declared many times by family, friends, or coworkers. That is, if you drop food on the floor, as long as you pick it up within five seconds, it’s still safe to eat.


Of course, if you do choose to believe the “5-second rule,” it usually depends on what kind of food you dropped, where it was dropped, and how hungry you are. Common sense would seem to indicate that the moment food comes in contact with the floor it can collect pathogens. But what does science have to say? Is there a risk, or is the rule valid?


Evidence in Favor of the 5-Second Rule

In 2014, a study out of Ashton University in England got widespread national press. A team under the direction of Anthony Hilton, professor of microbiology, reportedly found that there may be some scientific basis for the 5-second rule. True, they admitted that any initial impact immediately transferred at least a small number of bacteria from the floor to the food. However, dry foods picked up far fewer pathogens than moist foods, which in turn contained 10 times more bacteria when left on the surface for 30 seconds compared to 3 seconds.


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From these meager findings, Ashton University’s PR team concluded that “researchers prove the five second rule is real” in the title of a press release. In that statement, Professor Hilton proclaimed:


The findings of this study will bring some light relief to those who have been employing the five-second rule for years, despite a general consensus that it is purely a myth...Our study showed that a surprisingly large majority of people are happy to consume dropped food, with women the most likely to do so. But they are also more likely to follow the 5 second rule, which our research has shown to be much more than an old wives' tale.


Journalists love this kind of study – one that takes a seemingly unscientific idea and prove or disprove it with rigorous analysis. Soon enough, major publications were headlining the study for audiences eager for food advice. Bloggers and influencers also ushered the findings through social media. Meanwhile, two TV shows on the Discovery Science Channel – MythBusters and The Quick and the Curious – took on the topic. What none of these media sources reported was that the Ashton study was conducted by undergraduate biology students and never published in a peer-reviewed journal.


Evidence Debunking the 5-Second Rule

Responding along more professional protocols, Donald Schaffner, Rutgers Professor of Food Science, took the pains to publish his dissenting study in the prestigious Journal of Applied and Environmental Microbiology. As described in a Rutgers University report, Schaffner’s team of microbiologists subjected the 5-second rule to rigorous scientific tests and interpreted the findings in a broader context.


Four different foods (watermelon, gummy candy, plain bread, and buttered bread) were dropped onto four different surfaces (steel, ceramic, wood, and carpet) that were contaminated with bacteria. Each food remained on each surface for 1, 5, 30, and 300 seconds before being tested. As already reported by the Ashton study, sure enough, the longer the food was in contact with the germy surface, the more contaminated it became.


But here’s the catch: every food that fell on every surface was contaminated instantly upon contact, no matter how long it remained on the surface. Significantly, the transfer of bacteria is affected most by the amount of moisture in the food. Furthermore, the less absorbent the surface, the easier the transfer (this may come as some surprise to those who envision carpeting infested with invisible bugs). In fact, the nature of the food and the surface are more important to contamination rates than the duration of contact.


Schaffner’s study concluded that the 5-second rule is a gross oversimplification of what really happens when bacteria transfer from surface to food. No matter how fast you pick up that chocolate chip cookie, you will pick up bacteria with it.


The 5-Second Rule Is NOT a Food Service Best Practice

In your own home or private office, you certainly have the right to practice the 5-second rule and suffer any subsequent consequences. However, since bacteria obey no grace period, customers do have their own right to expect a “zero-second rule” at commercial food service operations.


In fact, CDC research has found that surface cross-contamination was the sixth most common contributing factor in 32 outbreaks of foodborne illnesses. Other studies conducted in the last few years also discourage adherence to the 5-second rule. So clearly, serving dropped food of any sort is simply unacceptable in any establishment catering to the public.


Perhaps a blog post from Synergy Restaurant Consultants put it best:


When you have the responsibility of serving the public, there is no room for the risk involved with the five-second rule. Serving or consuming food dropped on the floor or contaminated on another surface still poses an infection risk that is dependent on the bacteria present, and therefore, unsafe for food service. If you are at work, anything that is contaminated needs to be thrown away; however, what you choose to practice in your own home is up to you!


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