Five Second Rule: Real or Myth?

The mythical 5-second rule holds that food dropped on the floor may still be safely consumed provided it is picked up within five seconds. Results from studies on the topic indicate that other factors may play a bigger role in the transfer of bacteria than merely time spent on the floor.

Five Second Rule

Paul Dawson, a professor of food science at Clemson University, recently revived debate on the so-called five second rule by publishing a summary of research on the topic. Dawson’s article begins by posing the question “When you drop a piece of food on the floor, is it really OK to eat if you pick up within five seconds?”

Dawson highlights a 2007 study by his lab at Clemson University, which published a peer-reviewed journal paper on the topic. The lab used a variety of conditions to measure the transfer of food from floor surfaces. Tile, carpet, and wood surfaces were inoculated with Salmonella. Bread and bologna were placed on the different tiles for 5, 30, and 60 seconds. The tests were repeated with bacteria residing on the surfaces for 2, 4, 8, and 24 hours.

That study found that the amount of time had less of an impact than the amount of bacteria on the surface. Carpet fared the best among the different surfaces, transferring only 1% of bacteria, as opposed to as much as 70% for tile or wood. “The overall amount of bacteria on the surface mattered more, and this decreased over time after the initial inoculation,” Dawson concluded.

Other Tests

Dawson was not the first to investigate the five-second rule. In 2003, a high school student tested the theory by inoculating floor tiles and placing food on the surface for varying amounts of time. That test did find that bacteria transferred to food within 5 seconds, but the amount of bacteria wasn’t specified.

A more recent 2014 study out of the UK, also noted that moist foods were more likely to pick up bacteria than their dry counterparts. An researcher from that study concluded that carpeted surfaces were least likely to transfer bacteria, and that “which bacteria are present on the floor” is a major factor.

The Five-Second Rule was also featured on the popular television series Mythbusters. The team used moist pastrami and dry crackers for durations of 2 and 6 seconds. They concluded that all food picked up bacteria from the floor regardless of the amount of time, and that more bacteria was transferred to the wet pastrami than the dry crackers. “As far as I can tell, time didn’t seem to be a factor,” co-host Jamie Hyneman said.

Bottom Line

The Five-Second Rule has been put to test under a variety of conditions more more than a decade. Bacteria can transfer to food in a matter of seconds, but type of surface, moistness of food, and prevalence of bacteria on the target area are of greater significance than number of seconds of contact.