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.

'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 percent of women and 56 percent 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.
 

Restaurants and the 5-Second Rule

Robert Romaine first heard the five-second rule when he became a San Diego County health inspector, a job he held for more than 25 years. "I don't think anyone in the restaurant business really believes the five-second rule, but restaurant operators are concerned about the bottom line. So they might be reluctant to throw away food, even though they know the risk."

Romaine says violators are unlikely to get caught. "When a health inspector is in a restaurant, everyone is on their best behavior."

"If the food is dry, and there's no stickiness to it, it's less likely that bacteria will stick to it but in most cases we're talking about a $20 steak or a piece of fish that's not dry," Romaine tells WebMD. "If it's dry food, then we're just talking about filth, like hair or whatever is on the soles of shoes."

He is now a food safety consultant and culinary instructor at The Art Institute of California in San Diego. "We teach students that any surface, especially floors, should not be considered clean, and any food that comes in contact with it is trash."

That includes counters that have been washed and sanitized. If the precaution sounds extreme, consider the potential for damp floors and what might be on the shoes of a worker who walked her dog or used the restroom before coming to work. Then someone lifts a carton of produce from the floor and sets it on the counter. Maybe you don't want to eat food that has fallen on that counter.

A Smorgasbord of Opinions

Until further studies are done, there's no consensus on how safe it is to eat dropped food. Foodborne illnesses are not serious for most of the 76 million Americans who contract them every year. But, according to the web site of the CDC's National Center for Infectious Diseases, it's estimated that of those cases, 300,000 people are hospitalized, and 5,000 die. Most deaths occur among susceptible populations that include small children, the elderly, and people with weakened immune systems.

"I still pick up food off the floor," says Agle, "but I'm not in the susceptible population. I think the take-home message is that floors are generally clean but if there are microorganisms present, they will transfer in less than five seconds."