Show me the study on the five second rule

Seems like everyone I know if sending me this news story, declaring that the five second rule is real. The reports claim that there is truth to the matter that food picked up earlier is safer.

First of all, I can’t find the actual study they’re all citing. All I can find are press releases. Was this peer reviewed? Where are the methods? Come on!

But this also depends on what you mean by “safe”. Personally, I don’t care much about this kind of stuff at all. I’m fine eating food I dropped on the floor.

But here’s an actual, peer-reviewed study on the subject. Food scientists conducted three experiments to find out what happens when the five-second rule comes up against Salmonella typhimurium, a fairly common, but nasty bacterium that can cause wretched diarrhea and vomiting.  They tested how well Salmonella survived on wood, tile, and carpet, and they tested how well it transferred from these surfaces to either bologna or bread.  They found that bacteria were still alive after four weeks on dry wood, tile, or carpet, and enough of the bacteria survived to be able to transfer to food.  Next, the scientists tested how much time it took for the bacteria to transfer from these different floor surfaces to the food.  The worst offender of the five-second rule was bologna on tile.  Over 99% of the bacterial cells transferred from the tile to the bologna after just five seconds of the bologna hitting the floor!  Transfer from wood was a bit slower (5 to 68% of the bacterial were transferred) and transfer from carpet was actually not very successful.  After hitting the carpet, less than 0.5% of the bacteria transferred to the bologna.  When they did transfer, bacteria moved to the food almost immediately upon contact.  By five seconds, it was too late.  Other bacteria, like Campylobacter and Salmonella enteritis, also can survive well on formica, tile, stainless steel, wood, and cotton cloths, so if you listen to the microbiologists, you can never be too careful about cleaning things up in the kitchen, and you also can’t trust the five second rule. Bacteria that can make you sick can survive on the floor or other surfaces for a long times, and they can contaminate other foods that touch them for only a few seconds.

Bacteria aren’t the only thing that could make you sick when your food hits the floor.  A peer-reviewed study of pesticides on household surfaces shows that these toxic chemicals can also transfer to foods like apples, bologna, and cheese.  The pesticides seem to take a little longer than bacteria, though.  The average pesticide was only 1% efficient in transferring over to the food at the one minute mark, but up to 83% transferred if it was left on the floor for 60 minutes.  Applying more force to the food (like throwing it against the floor) also resulted in more pesticide getting on the food, up to 70% at ten minutes on hardwood flooring when bologna was squished with a 1500 g force.

I’ll update this post if someone sends me the actual study everyone is so excited about. Cause these studies are pretty good, and I trust their findings at the moment.

Please note that I’m not saying you should freak out about food dropped on the floor. I’m just saying that the five second rule seems like a myth to me.



Parts of this post were extracted from DON’T SWALLOW YOUR GUM! by Aaron Carroll, MD and Rachel Vreeman, MD copyright © 2009 by the author and reprinted with permission from St. Martin’s Griffin, an imprint of St. Martin’s Press, LLC

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