Don’t act like you’ve never done this before: You open a bag of chips and reach in to grab one. But drat! When you lift the salty snack to your lips, somehow you miss your mouth, and it falls to the floor. “Oh, well. Five-second rule,” you say as you pick up the chip and pop it into your mouth.
But according to biology experts at Loyola University in Illinois, the five-second rule—the notion that if you pick something off the floor quickly enough, it won’t be contaminated—has no basis in fact.
“A dropped item is immediately contaminated and can’t really be sanitized,” said Jorge Parada, medical director of the infection prevention and control program at Loyola University, in a statement.
But wait—what about the research from Connecticut College a few years back that found dropped food was still safe to eat even after 30 seconds? Two student researchers tested the bacterial contamination on apple slices and Skittles after being on the floor for 5, 10, 30, and 60 seconds. They found that no bacteria was present on either the wet or dry food for up to 30 seconds. So which is it—30 seconds or 0?
According to research published in the Journal of Applied Microbiology, it’s the latter. In the 2007 study, researchers at Clemson University tested bologna and bread on various surfaces that had been contaminated with salmonella 28 days before. They found that after dropping the food onto tile, 99 percent of bacterial cells contaminated the food immediately.
Parada agrees with Clemson’s research, explaining that an item can still pick up 1,000 bacteria instantly. While it would normally take approximately 10,000 bacteria to get infected, it’s worth being extra careful, especially those who have sensitive immune systems. As C. Claiborne Ray wrote in the New York Times of the salmonella study, “There were still thousands of the bacteria per square centimeter on the surfaces after 24 hours. As few as ten salmonella bacteria can cause gastroenteritis.”
The degree of contamination also depends on the type of food one drops. Hard foods, such as Skittles, are less likely to become contaminated within seconds compared with, say, a hot dog or a slice of bologna. The type of surface that the food falls on also plays a role. For example, in the Clemson study the food that fell onto the tiled surface picked up a plethora of bacteria, while the carpet food, somewhat surprisingly, picked up an insignificant amount.
So what’s a desperately hungry person to do next time that snack drops the floor? Said Parada: “When in doubt, throw it out.”