Forbes: A new study found some truth to the "five-second rule," which suggests it's safe to consume food that has touched the floor as long as its within the five-second limit.
But take this with a grain of salt. The study doesn’t appear to be peer-reviewed or published anywhere. We need other researchers to have a chance to review these results and then re-do the experiment before we can be sure it’s OK to eat that bagel you just picked up.
Read more here.