The Five Second Rule Has Been Supported by Science, but You Still Shouldn't Use It
Students at the Aston University's School of Life and Health Sciences have found that food picked up just seconds after being dropped on the floor is less likely to contain bacteria than food left for a longer period of time.
Everyone with a solid case of the munchies who has dropped a Doritos chip will quickly recognize that these findings support the ever-popular five-second rule. The tidbit of folklore provides that food snatched from the floor no greater than five seconds after its tumble is safe to consume, no Pepto required.
Aston's method was straightforward enough. They measured the transfer of E. coli and Staph bacteria from a variety of indoor flooring material to toast, pasta, a biscuit and sticky candy (wet gummy bear?) when contact was maintained from 3 to 30 seconds.
The results showed time was a significant factor in the amount of bacteria that ends up on your food, and that the type of flooring also has an impact. Carpet is safest, and bacteria is most likely to transfer from laminate or tile surfaces. The findings have popped up on food blogs around the country as an endorsement for the five-second rule.
But wait a minute.
A 2007 study from Clemson University also examined the efficacy of the five-second rule and said no dice. That study used multiple floor surfaces, toast, and for good measure, slices of bologna, and determined that while a longer period of contact contributes to higher bacteria transfer, a good bit of contamination (150 to 8,000 bacteria) can occur in under five seconds.
The differences in the studies could be attributed to variation in the methodology, errors or both. And the Aston study reveals that their data has yet to be peer reviewed, and is still preliminary. So for now, I'm trusting the Clemson guys, if only because eating off the floor is a little gross. Whatever decision you make for yourself, know that you're gambling with your gut. And besides, if food is sitting on your floor for more than five seconds, you should probably get a dog.