Scientists Just Tested the ‘5-Second Rule’

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You’ve probably heard of the five-second rule: If you drop some tasty item of food, but can scoop it off the floor within five seconds, there isn’t enough time for bacteria to get on it and it’s a-okay to eat. It’s a piece of folk wisdom that seems to transcend class and geography, embraced by a subset of C-suite executives in Manhattan and ravenous elementary students in the heartland alike.

Now, hardly anyone is a five-second-rule fundamentalist — even steadfast adherents to the rule probably aren’t going to eat a slice of pizza they drop cheese-side-down on a carpet, regardless of how quickly they can grab it. But many people, myself included, are willing to eat food off the floor. Is this gross? Are we gross?

Researchers are beginning to study this question in earnest, and a new study published in the journal Applied and Environmental Microbiology offers some disappointing news: No, it doesn’t take five seconds for bacteria to get on food.

The authors, Robyn Miranda and Donald Schaffner of Rutgers University, point out, there are just three studies on this subject that they are aware of, two of them shared via press releases but otherwise unpublished. To help fill this gap, the researchers left “watermelon, bread, bread with butter and gummy candy” on a variety of different surfaces contaminated with the Enterobacter aerogenes, which is a foodborne bacteria “with attachment characteristics similar to Salmonella,” for one, five, 10, or 300 seconds.

Unfortunately, it took less than a second for some bacteria to transfer, meaning that there’s no guarantee your potato chip will be bacteria-less even if you instantly grab it off the floor.

On the bright side — unsurprisingly — longer time in contact with the contaminated surface was correlated with more bacteria transfer, meaning a higher chance of some sort of infection in a real-world setting. Plus, “other factors including the nature of the food and the surface area are of equal or greater importance” — specifically “Carpet has very low transfer rates, compared with tile and stainless steel, whereas transfer from wood was more variable.”

What it comes down to is that “The 5-second rule is a significant oversimplification of what actually happens when bacteria transfer from a surface to food.” Who would have thought a rule you likely learned from a fellow kindergartner isn’t fully backed by science?