News

Testing the Five-Second Rule

Researchers in Britain show that picking up dropped food in less than five seconds carries less risk

March 17, 2014
GETTY IMAGES

An Ashton University study found that food dropped on a carpet is less likely to contain germs than food dropped on laminate and tiled surfaces.

You may have seen a friend drop food the on the floor, pick it up, and eat it, while declaring, “Five-second rule!” The old adage says that food dropped on the floor for five seconds or less is still likely to be clean. But is that true?

Students at Britain’s Ashton University, led by microbiology professor Anthony Hilton, tested the rule and found it to have some scientific basis. The study’s results show that food dropped for five seconds is less likely to contain bacteria than if it sits there, according to Hilton. Some of the results were published in a news release on Ashton University’s website.

The students also found that the type of flooring where the dropped food lands has an effect. Bacteria are least likely to transfer from carpeted surfaces. It’s most likely to transfer from laminate or tiled surfaces when moist foods make contact with them for more than five seconds.

There is still a risk of infection if certain bacteria are present on the dropped surface, so consumers should still be cautious. “However, the findings of this study will 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,” Professor Hilton said in a statement.

E. coli is a common germ that can cause diarrhea, vomiting, and cramps. Usually people recover from the infection in five to ten days, but it can also cause more severe complications.

GETTY IMAGES
E. coli is a common germ that can cause diarrhea, vomiting, and cramps. Usually people recover from the infection in five to ten days, but it can also cause more severe complications.

Will You Eat That?

To test out the rule, the Ashton University students dropped toast, pasta, biscuits, and candy onto a variety of indoor floor types that had been exposed to two common bacteria, Escherichia coli (E. coli) and Staphylococcus aureus. They measured how much of the bacteria transferred to the food when it was left on the floor for durations that ranged from three to 30 seconds. The university has not yet released the complete study.

The research team at Ashton also surveyed 500 people to find out who employs the five-second rule. Of the people surveyed, 87% said they would eat food dropped on the floor, or have done so in the past. Of those people, the majority were women. “Our study showed . . . [people] are also more likely to follow the five-second rule, which our research has shown to be much more than an old wives' tale,” Hilton says.

Still, scientists say you should be careful about eating food dropped on the floor, especially if you don’t know the cleanliness of the surface. A video about the five-second rule embedded on npr.org from the Smithsonian’s website features molecular biologist Eric Schulze, who points out that one in six Americans get sick from food poisoning every year. “Eating food off the floor is a bit like playing Russian roulette with your gut,” Schulze says in the video.


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