Anyone who has eaten food that briefly fell on the ground and declared the "five-second rule" may be unhappy to hear that a group of researchers have proved that theory as false.

"The popular notion of the 'five-second rule' is that food dropped on the floor, but picked up quickly, is safe to eat because bacteria need time to transfer," says Rutgers University Professor Donald Schaffner.

However Schaffner, whose specialty is food science, and other Rutgers researchers have disproven the rule. The study found that moisture, type of surface and contact time all contribute to cross-contamination. According to the study, contamination happened in some cases in less than a second.

"We decided to look into this because the practice is so widespread," says Schaffner.

The study tested different surfaces, different foods and different contact times.

There were over 2,500 tests. Researchers say that they were able to conclude that rule is oversimplified and that bacteria contamination can happen instantaneously.

The study was published in the American Society for Microbiology's journal, Applied and Environmental Microbiology.