The Five-Second Rule: Truth or Fiction?

April 14, 2014

Hint: If you have to eat off the floor, do it fast and go for carpet.

We’ve all heard the “five second rule.” If you drop food on the floor, it’s OK to pick it up and eat it if you get it off the floor within five seconds. Eating food off the floor is not my thing, but if you have kids, you’ll hear the ‘rule’ at some point. This has actually been researched, as well as the subject of a Mythbusters´TV show. People are still studying this, and there has been recent research that supports the theory behind the five second rule. Now, don’t go running out and scooping your baloney sandwich up off the floor in three seconds flat, just so you can take a big bite—the jury seems split on this one.

The first published five-second research was done by a high-school intern at the University of Illinois in 2003. The intern conducted a survey and found that slightly more than half of the men and 70 percent of the women knew of the five-second rule, and many said they followed it. She did an experiment by contaminating ceramic tiles with E. coli bacteria, placing gummy bears and cookies on the tiles for five seconds, and then analyzing the foods. They had become contaminated with bacteria.

It’s not surprising that food dropped onto bacteria would collect some bacteria. But how much, and key to the five-second rule – how quickly?

In 2007, Clemson University published a study that put some real numbers on floor-to-food contamination. Their bacteria of choice were salmonella; the floor surfaces were tile, wood flooring and nylon carpet; and the test foods were slices of bread and bologna. (There’s your baloney sandwich…)

First, the researchers applied salmonella to the floor surfaces, in quantities which would be typical of badly contaminated food. Then, the researchers placed test food slices onto salmonella-painted surfaces for varying lengths of time, and counted how many live bacteria were transferred to the food.

On surfaces that had been contaminated with the bacteria eight hours earlier, slices of bologna and bread left for five seconds took up from 150 to 8,000 bacteria. Left for a full minute, slices collected about ten times more than that from the tile and carpet, and a lower number of bacteria from the wood. What do these numbers tell us about the five-second rule? Quick pick-up does mean fewer bacteria, but it’s no guarantee of safety. (There were still bacteria, after all.)

The latest study—just published this month—was undertaken by final year Biology students at Aston University in England. (Apparently, the five-second rule is international, who knew?) This latest study found that food picked up just a few seconds after being dropped was less likely to contain bacteria than if it is left for longer periods of time. These findings suggest there may be some scientific basis to the “five-second rule.”

The Aston researchers monitored the transfer of the common bacteria Escherichia coli (E. coli) and Staphylococcus aureus from a variety of indoor floor types (carpet, laminate and tiled surfaces) to toast, pasta, biscuit and a sticky sweet when contact was made from 3 to 30 seconds.

The results showed that:

  • Time is a significant factor in the transfer of bacteria from a floor surface to a piece of food; and
  • The type of flooring the food has been dropped on has an effect, with bacteria least likely to transfer from carpeted surfaces and most likely to transfer from laminate or tiled surfaces to moist foods making contact for more than five seconds.

Consuming food dropped on the floor still carries an infection risk, as it very much depends on which bacteria are present on the floor at the time; however the Aston researchers felt that the findings of their study would “bring some light relief to those who have been employing the five-second rule for years, despite a general consensus that it is purely a myth.” The Aston study concluded, “We have found evidence that transfer from indoor flooring surfaces is incredibly poor with carpet actually posing the lowest risk of bacterial transfer onto dropped food.”

The Aston team also carried out a survey of the number of people who employ the five-second rule. The survey showed that:

  • 87% of people surveyed said they would eat food dropped on the floor, or already have done so;
  • 55% of those that would, or have, eaten food dropped in the floor are women; and
  • 81% of the women who would eat food from the floor would follow the 5 second rule.

The professor in charge of the study added: “Our study showed that a surprisingly large majority of people are happy to consume dropped food, with women the most likely to do so. But they are also more likely to follow the five-second rule, which our research has shown to be much more than an old wives’ tale.”