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Scientists Did a Serious Analysis of the Five-Second Rule, and Here's What They Found

A group of researchers from Rutgers University has set out to prove—using actual scientific methodology—that the five-second rule really is a bunch of malarkey, after all.

by Alex Swerdloff
13 September 2016, 9:00am

Photo via Flickr user Johnath

Some rules are rules. And some rules are, well, self-justifying constructions that no one really believes are legit—but people follow them anyway, with a wink and a nod. Atop the second category is the so-called "five-second rule." You know, the rule that lets you eat shit off the floor without major embarrassment.

It goes something like this: Food drops. A half-second assessment of the surface upon which the food dropped is made. Not a cesspool? Cool! Deep dive for food takes place, roughly before five-second mark. Gulp.

If someone else is present, yelling "Five-second rule!" prior to swallowing may save face—or just serve as a warning that you don't want to hear it. But no one truly believes eating food off the floor is advisable, do they? One regret-tinged dive after a damp, dust-bunny-encrusted sweetie will tell you all you need to know about the legitimacy of the five-second rule.

Still, the rule lives on.

We've reported before about one governmental agency—the Food Safety Information Council in Australia—who officially opined on the five-second rule. Their advice? Don't eat crap off the floor—especially moist food that falls on a funky surface.

READ MORE: Scientists Are Finally Taking a Stand Against the 'Five-Second Rule'

But now a group of researchers from Rutgers University has set out to prove—using actual scientific methodology—that the five-second rule really is a bunch of malarkey, after all.

MUNCHIES reached out to Dr. Donald Schaffner, a professor of food science at Rutgers and co-author of the study, who explained his motivation: "Several years ago, colleagues from Aston University in the UK issued a press release based on some research they had done on the topic. As someone who does research in cross-contamination, I'm very interested in this sort of research. I was very disappointed to learn that there was no peer-reviewed articles behind the above referenced press release, and all that university could provide was a PowerPoint presentation."

When Dr. Schaffner sat down with a graduate student, Robyn C. Miranda, to examine the topic, all they could find was "one other peer-reviewed study on the topic, as well as an episode of the MythBusters TV show, among others."

Schaffner and Miranda's new report, published in the American Society for Microbiology's journal, Applied and Environmental Microbiology, shows that moisture, type of surface, and contact time all factor in—not only to the level of grossness, but also to whether or not you will get violently ill thanks to your reliance on the five-second rule. The results of their experiments reveal that cross-contamination can begin in less than one second.

Admit it: Your diving skills may be good, but they're not that good.

Here's the deal: The researchers tested four surfaces, four foods, and four contact times to see whether Enterobactor aerogenes—a "cousin" of salmonella—would transfer from floor to food. All in all, 128 scenarios were replicated 20 times each. Think watermelon on carpet, bread and butter on ceramic tile, gummy candy on wood floor, plain bread on ceramic tile. The foods were tested for contamination at one second, five seconds, 30 seconds, and 300 seconds. Over 2,500 measurements were taken.

READ MORE: I Eat Food off the Floor All the Time, and I'm Proud of It

The results confirmed what you probably always thought: Moist foods don't fare well after a trip to the grimy, smelly, bacteria-encrusted floor. Watermelon fared worst, gummy sweets best.

"Transfer of bacteria from surfaces to food appears to be affected most by moisture," Dr. 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."

Weirdly enough, though, carpet had lower transfer rates as compared to tile and stainless steel.

This may seem counterintuitive, but as Dr. Schaffner explains, "The topography of the surface and food seem to play an important role in bacterial transfer." Perhaps the peaks and valleys in carpeting provide some protection against bacteria transfer.

Beware of unappetising fuzz, though.

Schaffner told us, "I'm not sure whether anyone will behave differently as a result of my research, but I'm confident in the fact that we have made a serious scientific contribution and may cause people to think a little bit more carefully the next time the pick food up off the floor."

Maybe. Maybe not.