Why the five-second rule, sadly, makes no sense

ice cream accident
CC BY 2.0 Johnathan Nightingale

Scientists decided to put the old five-second rule to the test, to prove once and for all whether there is any truth to it.

You’re heard of the ‘five-second rule’? The widely accepted belief says it’s safe to eat anything that hits the floor or ground, as long as you pick it up within five seconds of falling. There has been considerable debate about the accuracy of the rule, which finally led scientists to put it to the test.

The resulting study, which was published online in Applied and Environmental Microbiology, found that food does get contaminated immediately upon contact with the ground, but the degree of contamination depends on the type of food, the surface texture, and, obviously, the length of time it’s there.

Researchers sprayed the same amount of bacteria on a four different surfaces – wood, carpet, tile, and stainless steel – and let it dry to reach the same level of concentration. Four types of food – watermelon, bread, bread with butter, and gummy candy – were dropped from a height of 12.5 centimeters (5 inches) onto the surfaces and left for four different contact times (less than 1 second, 5 seconds, 30 seconds, and 300 seconds, which is 5 minutes).

They found that wetter foods (watermelon) pick up bacteria more quickly than dry foods (gummy candy). Bread, with and without butter, took the same amount of time to pick up bacteria. Surprisingly, carpet was found to be the cleanest surface, likely because its rough texture minimizes contact with food.

So the five-second rule doesn’t work, but I don’t think it’s going to change the way dropped food is handled in my house. The baby crawls around looking for stray raisins and the older kids certainly wouldn’t give up on a fallen ice cream cone that easily. When I think of all the other surfaces our food touches, particularly unpackaged produce on its journey from field to table, I have to say the floor doesn’t scare me that much, no matter what the scientists say.

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