Five-second rule

A common superstition, the five-second rule states that food dropped on the ground will not be contaminated with bacteria if it is picked up within five seconds of being dropped. Some may earnestly believe this assertion, whereas other people employ the rule as a polite social fiction that will allow them to still eat a lightly-contaminated piece of food, despite the potential reservations of their peers. 

 Dr. Jorge Parada, medical director of the infection prevention and control program at Loyola University Health System. Parada cautioned that as soon as something touches an unclean surface, it picks up dirt and bacteria.

"A dropped item is immediately contaminated and can't really be sanitized," said Parada in a health system news release. The amount of bacteria and what type of microbes are involved depend on the object that is dropped and where it falls, he added.

Rising off contaminated items with water may not clean them entirely, but it could significantly reduce the amount of bacteria on it, Parada noted.

"Maybe the dropped item only picks up 1,000 bacteria, but typically the inoculum, or amount of bacteria that is needed for most people to actually get infected, is 10,000 bacteria -- well, then the odds are that no harm will occur," he said.

That's not the case for items that are "cleaned" by licking them off or putting them in the mouth.

"That is double-dipping," Parada explained. "You are exposing yourself to bacteria and you are adding your own bacteria to that which contaminated the dropped item. No one is spared anything with this move."

     People who follow the "five-second rule" may be better off sticking to the phrase, "when in doubt, throw it out."