via Forbes.com

2 seconds, 5 seconds, 30 seconds–we all have heard that there is the “___ second rule” for dropping food on the floor and being allowed to eat it. Somehow it became the social norm to declare that if the food is picked up before a certain amount of time, it can be safely eaten. How scientifically accurate is this rule?

Paul Dawson, Clemson University researcher, published an article on this in the “Journal of Applied Microbiology” on testing this rule. First they tested Salmonella longevity on surfaces and found it could remain viable for up to 4 weeks. Next, they dropped food and picked it up in certain amounts of time lengths and 99% of the bacteria was transferred instantaneously. Of course, this experiment is flawed because it only tests the effects of Salmonella, and there are countless other types of bacteria thriving on surfaces.

Another study was done by Jillian Clarke at University of Illinois. She swabbed the University’s floors in many different locations two times and found both times that there was a minimal number of microorganisms present, which is attributed to the fact that the floors are dry and pathogens survive better in environments with moisture. Then gummy bears and cookies where dropped on both smooth and rough tiles that had a measured amount of E. coli. Results showed that a “large number” of cells from bacteria were transferred before 5 seconds. The issue with the publication of this study as that “large number” is not defined, so it is a subjective result. In addition, while the measured E. coli amount was designed to keep the experiment controlled, this denies information on whether the amount of bacteria on the floor is correlated to the speed in which the bacteria is transferred from floor to food.

Professor of Microbiology at Aston University , Anthony Hilton, conducted a study that tested a variety of different foods on different levels of “stickiness” on a variety of different floor types. They found that the longer the food was left on the floor, the more contaminated it was. Therefore this somewhat supports the 5-second rule, but more as a standard of how much bacteria you personally consider “too much” and if the amount gathered by 5 seconds is acceptable, since each second you wait the food is dirtier. It also determined that sticky food collects more bacteria, but carpet transfers the least amount of bacteria.

Many factors are usually considered before your pick up the food and pop it in your mouth. How expensive is the food? How delicious is the food? How questionable is the surface? How hungry are you? When it comes down to these, science may not play much of a role in your decision to give the dropped snack a second chance. Based on these experiments, the studies are not very large or well conducted, so it’s difficult to decide that your childhood of eating food within only 3 seconds has actually been harmful. But on the other hand, you’ve been doing it your whole life and turned out fine, so why change now? Just like drunk driving is a cause for accidents but doesn’t always cause accidents, you can’t determine the action is 100% going to be harmful. So should you reject the 5-second rule? In the words of Andrew, it’s “hard to say.”

Sources:

http://www.forbes.com/sites/alicegwalton/2014/03/14/amazingly-science-backs-5-second-rule-for-dropped-food/

http://www.webmd.com/a-to-z-guides/features/5-second-rule-rules-sometimes-

http://www.thenakedscientists.com/forum/index.php?topic=43243.0