We have all been there before when we accidentally drop a piece of food on the floor, but rush to pick it up as quickly as we can and pop it our mouth.

We do this under the pretense that there is no way germs can get on the food so quickly, so it must be safe to eat. This is known as the "five-second rule."

However, you might want to think twice before gobbling up the fallen food, because scientists found that there is no truth to the five-second rule at all. In fact, it takes less than a second for bacteria to be transferred onto food once it is dropped on the ground.

Researchers at Rutgers University put the five-second rule to the test, picking up where other laboratories left off — since there have only been three studies conducted on the theory that has not been published in scientific journals — to come to their own conclusion regarding the popular notion.

Led by Robyn Miranda and Donald Schaffer, the team tested how long it took watermelon, bread and butter, plain bread and gummy candy to be contaminated after falling on surfaces that contained Enterobacter aerogenes, a bacteria similar to Salmonella. The surfaces included in the study were stainless steel, ceramic tile, wood and carpet.

Each piece of food was then tested on each surface for various periods of time. This included letting the piece of food remain on the ground for one second, five seconds, 30 seconds and 300 seconds. In total, there were over 100 different scenarios 20 different times.

Published in Applied and Environmental Microbiology, the researchers debunked the five-second rule, finding that the bacteria on the floor quickly transfers to food almost immediately. However, they found that more germs got on wet food (in this case, the watermelon) more than other types of food. This means moisture has a direct relationship to the spread of bacteria.

Those who do eat food after dropping it are better off only doing so when they drop their snack on carpet. The study found that more flat surfaces like stainless steel and tile had higher rates of cross-contamination than wood.

That doesn't necessarily mean that dropping chips on the carpet and then eating them means they are bacteria-free.

Of course, the longer the piece of food remains on the floor, the higher the rate of bacterial contamination.

"Although we show that longer contact times result in more transfer, we also show that other factors including the nature of the food and the surface are of equal or greater importance. Some transfer takes place 'instantaneously' at times <1 s, disproving the 'five second rule,'" the study authors conclude. 

Photo: Johnathan Nightingale | Flickr