From Science Daily:
Food picked up just a few seconds after being dropped is less likely to contain bacteria than if it is left for longer periods of time, according to the findings of research carried out at Aston University's School of Life and Health Sciences.
The findings suggest there may be some scientific basis to the '5 second rule' -- the urban myth about it being fine to eat food that has only had contact with the floor for five seconds or less. Although people have long followed the 5 second rule, until now it was unclear whether it actually helped.
The study, undertaken by final year Biology students and led by Anthony Hilton, Professor of Microbiology at Aston University, monitored the transfer of the common bacteria Escherichia coli (E. coli) and Staphylococcus aureus from a variety of indoor floor types (carpet, laminate and tiled surfaces) to toast, pasta, biscuit and a sticky sweet when contact was made from 3 to 30 seconds.
The results showed that: - Time is a significant factor in the transfer of bacteria from a floor surface to a piece of food; and - The type of flooring the food has been dropped on has an effect, with bacteria least likely to transfer from carpeted surfaces and most likely to transfer from laminate or tiled surfaces to moist foods making contact for more than 5 seconds.
Professor Hilton said: "Consuming food dropped on the floor still carries an infection risk as it very much depends on which bacteria are present on the floor at the time; however the findings of this study will bring some light relief to those who have been employing the five-second rule for years, despite a general consensus that it is purely a myth. We have found evidence that transfer from indoor flooring surfaces is incredibly poor with carpet actually posing the lowest risk of bacterial transfer onto dropped food.