No matter how fast you pick up food that has fallen to the ground, the microbes will still be able to contaminate it! Researchers from Rutgers University, a New Jersey University, denied the ‘five-second rule’, according to which ‘sometimes bacteria can move in less than a second’.

Humidity, type of surface and the time during which the object remains on the floor, Professor Donald Schaffner pointed out , contribute to cross-contamination. A process that, in some cases, would already start in less than a second.


Five seconds is more than enough for contagion! “The common idea of ​​the ‘five-second rule’ is that food that has fallen to the ground, but quickly recovered, can be eaten because bacteria needs time to move there.” Schaffner explained, who conducted the research with Robyn Miranda.

The tests were carried out on four different surfaces – stainless steel, ceramic tiles, wood and carpet – on which micro-organisms were present, and with four types of food (watermelon, bread, bread and butter, gummy sweets). The ‘shutter speeds’ were: less than a second, five seconds, thirty seconds and 300 seconds.


The discovery was also published in the journal Applied and Environmental Microbiology. Once all the possible scenarios had been analysed, it emerged that the watermelon was the most contaminated food, unlike the gummy candies.

“The transfer of bacteria from the surface to the food seems to be conditioned above all by the humidity”, said Schaffner. “Bacteria does not have legs, it moves with humidity and the more the food is moist, the more there is the risk that it moves”. A proportion also valid for the time the food remains on the ground. The lowest transfer rate was found on the carpet.

The ‘five-second rule’, therefore, would be only partially true: the more time the food remains on the floor and more germs can be transferred to it!