While the origin of this rule is not really known, it is believed that it may have come from the Mongolian ruler Genghis Khan, who would allegedly let food sit on the floor, based on the belief that anything prepared for him would always be good enough to eat.

Researches done 

According to a study published in the Applied and Environmental Microbiology journal, no fallen food can completely evade a contamination. But it also didn’t find more bacteria on a food that was left on the floor for a longer time period.

Experts say that the time period does not play as much of a role as the type of floor, and the composition of the food. For instance, carpeted floors are likely to have fewer bacteria than floors made of tile and stainless steel.

The risks associated 

Studies show that when you eat food off the ground, you expose yourself to bacteria such as e coli and salmonella. Both these bacteria are known to cause unpleasant side effects and diseases that could turn deadly. It is, therefore, advisable that whenever you drop your food, you use your discretion and not rely on the five-second rule.