Researchers debunk 'five-second rule': Sometimes bacteria transfer in less than a second

Researchers debunk 'five-second rule': Eating food off the floor isn't safe
Researchers found carpet has very low bacteria transfer rates compared with those of tile and stainless steel whereas wood's is more variable. Credit: Shutterstock/Joe Belanger

Turns out bacteria may transfer to candy that has fallen on the floor no matter how fast you pick it up.

Rutgers researchers have disproven the widely accepted notion that it's OK to scoop up and eat it within a "safe" five-second window. Donald Schaffner, professor and extension specialist in food science, found that moisture, type of surface and contact time all contribute to cross-contamination. In some instances, the transfer begins in less than one second. Their findings appear online in the American Society for Microbiology's journal, Applied and Environmental Microbiology.

"The popular notion of the 'five-second rule' is that food dropped on the floor, but picked up quickly, is safe to eat because need time to transfer," Schaffner said, adding that while the pop culture "rule" has been featured by at least two TV programs, research in peer-reviewed journals is limited.

"We decided to look into this because the practice is so widespread. The topic might appear 'light' but we wanted our results backed by solid science," said Schaffner, who conducted research with Robyn Miranda, a graduate student in his laboratory at the School of Environmental and Biological Sciences, Rutgers University-New Brunswick.

The researchers tested four surfaces - , ceramic tile, wood and carpet - and four different foods (watermelon, bread, bread and butter, and gummy candy). They also looked at four different contact times - less than one second, five, 30 and 300 seconds. They used two media - tryptic soy broth or peptone buffer - to grow Enterobacter aerogenes, a nonpathogenic "cousin" of Salmonella naturally occurring in the human digestive system.

Transfer scenarios were evaluated for each surface type, food type, contact time and bacterial prep; surfaces were inoculated with bacteria and allowed to completely dry before were dropped and left to remain for specified periods. All totaled 128 scenarios were replicated 20 times each, yielding 2,560 measurements. Post-transfer surface and food samples were analyzed for contamination.

Not surprisingly, watermelon had the most contamination, gummy candy the least. "Transfer of bacteria from surfaces to food appears to be affected most by moisture," Schaffner said. "Bacteria don't have legs, they move with the moisture, and the wetter the food, the higher the risk of transfer. Also, longer food contact times usually result in the transfer of more bacteria from each surface to food."

Perhaps unexpectedly, carpet has very low transfer rates compared with those of tile and stainless steel, whereas transfer from wood is more variable. "The topography of the surface and food seem to play an important role in bacterial transfer," Schaffner said.

So while the researchers demonstrate that the five-second rule is "real" in the sense that longer contact time results in more bacterial transfer, it also shows other factors, including the nature of the food and the surface it falls on, are of equal or greater importance.

"The five-second rule is a significant oversimplification of what actually happens when bacteria from a to food," Schaffner said. "Bacteria can contaminate instantaneously."

Explore further

Research suggests the five-second rule is real

More information: Robyn C. Miranda et al, Longer Contact Times Increase Cross-Contamination offrom Surfaces to Food, Applied and Environmental Microbiology (2016). DOI: 10.1128/AEM.01838-16
Provided by Rutgers University
Citation: Researchers debunk 'five-second rule': Sometimes bacteria transfer in less than a second (2016, September 9) retrieved 22 February 2019 from
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User comments

Sep 09, 2016
This "rule" was never, actually, a rule but just a base, vulgar, practice, by fools, to justify eating food dropped on the floor or ground. There was never any science claimed, except by the animals who wanted to eat off the floor. Anyone who ever believed otherwise is an idiot.

Sep 09, 2016
If this paper does not show you how meaningless progressive education is then you might be a Liberal!

Sep 09, 2016
Yup, this is not too much unlike today's public school students given " Achievement Awards" for just being! Oh yes, being class Valedictorian is way too exclusionary and needs to be eliminated lest others feel excluded!

Sep 09, 2016
Now science has gone to far.

It's a brave new world...

Sep 10, 2016
1. Gummy candy fallen from one's mouth onto any kind of floor has on each floor the highest and most rapid contamination rate.
2. Unwrapped gummy candy kept in a bowl for 30+ minutes in any room at a humidity of more than 55% equals the watermelon contamination intensity and rapidity on all floors. On wool carpets it surpasses it.
3. All foods get more rapidly contaminated on any kind of wet floor than on a dry floor. . Only the watermelon does not (it even gets less contaminated) ...

Conclusion: many students, scientists and professors can't even get the most simple and stupid kind of pseudo-study right. But we owe them much - for the great moments of amusement they made possible.

Sep 10, 2016
The 5 second rule is not real. I was unlucky once and was severely sick because of it. If the rule work for you then it's because you are lucky; because the place didn't have pathogenic organism on it.

If your food fall on place with lots of people, then be really really worried, you will certainly get sick if you pick that food up.

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