‘Five-second rule’ debunked

The journal of the American Society of Microbiology has released a report claiming that the notion of the ‘five-second rule,’ a popular idea that food remains mostly germ-free in the first five seconds of being dropped on the floor, is false.

Researchers at Rutgers University conducted the study, and food science specialist Donald Schaffner “found that moisture, type of surface and contact time all contribute to cross-contamination. In some instances, the transfer begins in less than one second,” according to Science Daily.

Schaffner worked with graduate student Robyn Miranda on the study, and together they tested four foods — cut watermelon, bread, buttered bread and gummy candy — on four surfaces — stainless steel, ceramic tile, wood and carpet. Surfaces were treated with Enterobacter aerogenes, a harmless cousin of Salmonella that occurs naturally in the human digestive system.

The New York Times reports, “The researchers tested four contact times — less than one second and five, 30 and 300 seconds. A total of 128 possible combinations of surface, food and seconds were replicated 20 times each, yielding 2,560 measurements.”

As one might expect, the study determined that the longer food rests on a contaminated surface, the more bacteria it picks up, so in a way, the five-second rule makes some sense. However, no dropped food sample came up bacteria-free. Additionally, high-moisture foods attract significantly more bacteria, so watermelon drew the most contaminants, and gummy candy drew the least. Surprisingly, carpet has very low bacterial transfer rates when compared to wood and stainless steel.

In response to the question of why people choose to believe the five second rule and eat off the floor, Rutgers professor and experimental psychologist William K. Hallman told the New York Times that people do not put every decision through a risk-benefit filter and instead rely on cognitive shortcuts called heuristics to help in their daily lives. However, these shortcut decisions are often based on “flawed assumptions or missing information…because germs are out of sight, the belief is there is no harm in picking up the M&M and popping it in your mouth,” according to the New York Times.

While eating off the floor doesn’t necessarily mean one will always fall ill, “People also do not recognize the symptoms of food-borne illnesses and tend to blame them on the last thing they ate, so they do not connect how their earlier actions might have made them sick,” the New York Times explains.

“The five-second rule is a significant oversimplification of what actually happens when bacteria transfer from a surface to food,” Schaffner says.Shaffner reiterates sentiments similar to the above comic:  “Bacteria can contaminate instantaneously.”