It's a global phenomenon: We drop something delicious on the floor, don't want to throw it out and so justify eating it with the “five-second rule”. That is, if something has been on an unclean surface for less than five seconds it won't have got dirty enough to stop us eating it. Nevertheless, most of us know there is nothing to it – what matters is how clean the floor is, and we probably feel a twinge of guilt popping that retrieved chocolate into our mouths.
Except it turns out the five second rule is true, sort of. Or at least it might be. Indeed, under some circumstances even those who tolerate longer floor times might be onto something. Aston University Microbiology Professor Anthony Hilton had final year students measure the collection of E coli and golden staph by toast, pasta, biscuits and sticky sweets on three indoor floor surfaces.
"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," said Hilton.
Unsurprisingly, the food texture matters – sticky foods collect bacteria almost immediately, while biscuits take longer. Floorboards transfer the most bacteria. However, Hilton's team found that, at least under the right conditions, contact time can also be important.
“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.”
Hilton also ran a survey that revealed how widely the significance of his work spreads. Asked if they would eat food off the floor 87% said yes, with the majority of these saying timing was important.
How much bacteria it is safe to consume varies widely depending on factors such as the strength of the immune system and the strain of pathogen. Some scientists argue we are becoming exposed to too few dangerous bacteria, preventing the development of antibodies so that when exposure does occur we are overwhelmed.
It should be noted, however, that the research has yet to be published in a peer reviewed journal, and until then the possibility that it is mere propaganda for the carpet industry must be considered. Hilton's findings contradict some previous research, including an ignoble winner. A more scientific study published in the Journal of Applied Microbiology agreed on the importance of the type of flooring, and found the transfer times were important for some floors and not for others.