The 5 Second Rule – A Scientific Examination

It’s a lazy Saturday and you’re at home having a leisurely lunch, watching YouTube on your phone while you eat a delicious bologna sandwich. The next thing you know, those crazy YouTube cats have made you laugh so hard that you drop your sandwich – what do you do? Do you throw the contaminated sandwich away? Or do you think to yourself “five second rule,” pick it up and continue eating?

Everyone knows the 5 Second Rule: if you drop food on the floor, it’s okay to eat, as long as you pick it up within five seconds. A researcher at the University of Illinois found that 56% of men and 70% of women surveyed had heard of this rule (or its alternative version, the 3 Second Rule), qualifying it as a legit Western Cultural Phenomenon.

So, is this real or what? Surprisingly, studies have given conflicting views as to what exactly the 5 Second Rule means for our health and welfare. Jillian Clarke, the researcher from U of Illinois found that food was contaminated within five seconds of being dropped onto ceramic tile inoculated with E. coli. She had some trials and tribulations in the course of her research – at first she was simply going to drop the food on the lab floor, but the lab floors turned out to be *too* clean. She also found that women tended to pick up and eat their dropped food more often than men, and that more E. coli was transferred to dropped food from rough tiles vs. smooth tiles. For this research she was awarded the prestigious/dubious Ig Nobel in Public Health in 2004.

Pop culture then took up the mantel of this important question, and experiments were performed on both Mythbusters and Food Detectives. These researchers found that bacteria sticks to food pretty much right away and it doesn’t matter how long you leave it there – the damage is done.


Image: A Thing of Beauty, Matt Reinbold, CC by 2.0

Researchers at Clemson University also set out to test the 5 second rule using the inveterate bologna sandwich. Their main after a series of experiments was not the now-unsurprising finding that if you drop food on the floor it picks up bacteria pretty much right away. What they also found was the fact that live bacteria actually lingers for a REALLY long time on surfaces such as tile floors or kitchen countertops. I think their preliminary research might have freaked them out a bit, as their Introduction highlights another study that found washing hands didn’t actually prevent bacteria transfer, but luckily ALSO found that drying hands after washing significantly mitigated this effect. Like Jillian, the Clemson crew found that rough carpet transferred less bacteria when compared with tile or wood.

The most conclusive research to date is from Prof Donald Schaffner, a food microbiologist from Rutgers. He led a two-year study, which also found that – you guessed it – dropped food = bacteria. It’s probably true that the faster you pick it up, fewer bacteria will get on your food, but still… yuck. Professor Schaffner told the New York Times, “on the record, I have eaten off the floor… [but] if I were to drop a piece of watermelon on my relatively clean kitchen floor, I’m telling you, man, it’s going in the compost.”

Featured Image: Spilled Strawberries, Rachel Glaves, CC by 2.0
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Laurie Breen

Laurie Breen is a freelance writer well-versed in research communications and grant writing. She received her Bachelors Degree in Psychology from Smith College and has worked previously at the University of Queensland's Centre for Clinical Research in Brisbane, Australia. Her favorite conversational topic is "antibiotic-resistant bacteria," making her a big hit at parties.