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'5-Second Rule' Rules, Sometimes

Experts explore whether it's safe to eat food that's made quick contact with the floor.
WebMD Feature
Reviewed by Louise Chang, MD

In households, restaurant kitchens, and almost anywhere people prepare or consume food, you'll occasionally hear someone call out "five-second rule." Whether it's uttered as a way for the speaker to let others know he's civilized, as an excuse to salvage expensive food, or as an incantation to ward off sickness, the meaning is the same: If food hits the floor and you snatch it up in less than five seconds, it's safe to eat."

Is the food really safe? Or should we throw it away or wash it off? WebMD talked to experts to find out what you should consider before swallowing this rule whole.

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'5-Second' Research

Yes, someone really has conducted a scientific study of the five-second rule. It was the project of high school senior Jillian Clarke during a six-week internship in the food science and nutrition department at the University of Illinois at Urbana-Champaign. Meredith Agle, then a doctoral candidate, supervised the study.

"Jillian swabbed the floors around the University in the lab, hall, dormitory, and cafeteria to see how many organisms we could isolate," Agle tells WebMD. "We examined the swabs, and there were very few microorganisms. That surprised me. I told her to do it again."

The results were the same. Agle has since earned her doctoral degree and is a scientist in new product development for Rich Foods in Buffalo, N.Y. "I think the floors were so clean, from a microbiological point of view, because floors are dry, and most pathogens like salmonella, listeria, or E. coli can't survive without moisture."

To control the study, cookies and gummi bears were placed on both rough and smooth sterile tiles covered with measured amounts of E. coli. "We did see a transfer of germs before five seconds," Agle tells WebMD. "We were dealing with a large number of cells."

All bets are off when it comes to carpet, damp floors, gum, or ice cream, as these were not included in the study.

Clarke also conducted a survey in which 70% of women and 56% of men said they were familiar with the rule. Women were more likely to invoke it. Not surprisingly, people are inclined to eat dropped cookies and candy more often than dropped broccoli and cauliflower.

For her work, Clarke was awarded an Ig Nobel prize in 2004 at Harvard University. Ig Nobel prizes recognize "research that first makes you laugh, then makes you think." Also honored at the ceremony was the inventor of karaoke music.

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