Scientific Research Shows The Five Second Rule Is True

The five second rule is one of those schoolyard myths that seems to make no sense as you learn more about germs and bacteria, but as it turns out the playground talk was true- if you pick food up off the ground within five seconds it’s (relatively) safe to eat.
Students from Aston University in Birmingham, England, led by microbiology professor Anthony Hilton, conducted a study that focused on how E. Coli and Staphylococcus aureus are transferred to many different foods from many different floor types.
They found that "time is a significant factor in the transfer of bacteria from a floor surface to a piece of food", meaning it often takes longer than five seconds for the bacteria to adhere to the food.
A note by Professor Hilton:

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.