When the '5-Second Rule' Works (and When it Doesn't)

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Ever wonder if it’s really safe to eat food quickly after dropping it on the ground?

Science suggests that it may actually be alright to do so -- however, there are conditions -- because it all depends on what you drop and where you drop it. But given the proper circumstances, you can have reasonable faith that the so-called "5-second rule” works to keep illness at bay.

That's also the view presented in a report on the Discovery Science Channel called the “The Quick and the Curious.” And, as you might expect, time plays a role in determining what's considered edible, and what's considered risky.

E. coli, Salmonella and Listeria thrive in wet places, and they suck up nutrient-rich water needed in order to reproduce. So when food is left on the ground or dirty surface for 30 seconds, according to Discovery 10 times the bacteria jumps on moist food than if left for just three seconds. But as far as bacteria goes, the 5-second rule stands for food hitting dry surfaces, according to veteran San Diego County health inspector Robert Romaine.

“If the food is dry, and there’s no stickiness to it, it’s less likely that bacteria will stick to it,” Romaine said. “If it’s dry food, then we’re just talking about filth, like hair or whatever is on the soles of shoes.” What this really means is that you're dealing with what you can see -- and can possibly brush or blow off -- as opposed to bacteria which you can't see.

And then there are surfaces. The Discovery video report also stated that some bacteria will always climb onto fallen food, but that fewer germs can migrate from rugs than linoleum. That's due to the small, separated tufts on rugs, upon which less surface area of food makes contact.

Clemson University Professor Paul Dawson backed up this claim in a 2006 study in which he placed bologna and bread on Salmonella-inoculated squares of carpet, tile and wood for various amounts of time. He found that 48 to 70 percent of the bacteria attached to the food from the tile and wood. Comparatively, the food was found to have had less than one percent of the bacteria from the carpet.

According to Dawson, "It looks like what’s at issue is less how long your food languishes on the floor and much more how infested with bacteria that patch of floor happens to be." A similar study from Aston University found similar results. This U.K. study found that 87 percent of people asked had no problem eating fallen food, and that 55 percent were women.

One should still display caution, Ruth Frechman, MA, RD, tells WebMD. "Bacteria are all over the place, and 10 types -- including E. coli -- cause foodborne illnesses, such as fever, diarrhea, and flu-like symptoms."

About 76 million Americans contract foodborne illnesses each year, according to the CDC. And about 300,000 are hospitalized, while 5,000 die.

"Err on the side of safety," Frechman says. "At least, wash it first."