It is not known when exactly the "five-second rule" originated, but some historians claim that its origins go as far back as... Genghis Khan himself. Allegedly, the shaker of the universe said that food remains edible if it remains on the ground for no more than five hours. Through the centuries, five hours transformed into five seconds. However, it is difficult to believe this, if only because the Mongols hardly carried clocks in the modern sense of the word and used other ways of measuring time.
In an attempt to answer the question of whether time on the floor plays any role at all for microbes, scientists dropped a slice of watermelon, bread, buttered bread and chewy marmalade alternately on four types of surfaces: stainless steel, ceramic tile, wood and carpet. After letting the food sit on the surfaces for 1, 5, 30 and 300 seconds, the experts collected all the samples and studied the amount of bacteria they contained. Particular attention was paid to enterobacter cloacae, a bacteria that causes intestinal disorders and inflammation.
The results showed that the "five-second rule" was not as meaningless as it seemed at first glance. The longer food is on the ground, the more bacteria it collects. True, in this case it is only a matter of whether millions or tens of millions of microorganisms end up on the food: even the fastest and most nimble person will not have time to pick up the food before microbes infest it.
In addition, the amount of bacteria on food is affected by both its structure and the surface on which it falls. For example, bacteria collects faster if wet food falls on a hard, even surface. Therefore, a piece of watermelon that fell on stainless steel collected the most bacteria. Conversely, bread lying on the carpet contained the least bacteria.