Have you ever experienced that you pick up the food dropping on the floor and keep eating it? Yes, I have. Because I think I pick up them immediately and it seems that food looks good. Also, I’ve heard of “three-second rule”, which also has other names like “five-second rule” or “ten- second rule” — food (or sometimes cutlery) dropped on the ground will not be significantly contaminated with bacteria if it is picked up within three (or five or ten) seconds of being dropped. In my memory, this rule comes from Japan. And before I searching the background of this rule, I believe this rule is real and scientific.

However, in fact, this rule is just created by a girl of the Chicago High School for Agricultural, Jillian Clarke who was the winner of Public Health of the 2004 Ig Nobel Prize. A report of DailyMail pointed out that the researchers of Manchester Metropolitan University tested five food items, which were bread with jam, cooked pasta, ham, a plain biscuit and dried fruit, to see whether the three-second rule could be true. They dropped these food items on the floor and left them for 3, 5, and 10 seconds intervals to see whether the items will sustain bacterial growth in the interval. Both the ham, a salty product, and the sugary bread and jam fared well in the test. After the study, researchers found that the food with a high salt or sugar content were safer to eat after being retrieved, as is less chance of harmful bacteria surviving on such items. Thus, the report think that three-second rule fit the food containing the most sugar and salt.

Does it mean that three second rule real? From my perspective, No! I think although there is a research show the conclusion, it still has possibility that the study is false positive. Because the research was only done by once, which means there is no repeated experiment. Also, there is no other report or study supporting this conclusion. What’s more, even though the research shows that the condition of food with high salt and sugar doesn’t fit the environment for bacteria to reproduce
, dropped food would be sticked by the bacteria on the floor. So the existed bacteria also harm to human body. Hence, the the transfer of bacteria between floor and food is also very important.

Rutgers researchers also do the research in order to turn out bacteria may transfer to candy that has fallen on the floor no matter how fast you pick it up. “The researchers tested four surfaces — stainless steel, ceramic tile, wood and carpet — and four different foods (watermelon,
bread, bread and butter, and gummy candy). They also looked at four different contact times — less than one second, five, 30 and 300 seconds. They used two media — tryptic soy broth orpeptone buffer — to grow Enterobacter aerogenes, a nonpathogenic “cousin” of Salmonella naturally occurring in the human digestive system.” After replicating 128 scenarios 20 times each, which means they yielded 2560 measurements (enough repeated experiment!!!) They got the result that watermelon had been contaminated most heavily and gummy candy has been contaminated least heavily. This result demonstrates that moisture is the key factor of transfer of bacteria from surfaces to food appears. Donald Schaffner, professor and extension specialist in food science, said “Bacteria don’t have legs, they move with the moisture, and the wetter the food, the higher the risk of transfer. Also, longer food contact times usually result in the transfer of more bacteria from each surface to food.” In addition, they got an unexpected result that the topography of the surface and food also play an important role in bacterial transfer. The flatter floor makes more bacteria transfer successfully. So although longer contact time results in more bacterial transfer, it also shows other factors, like moisture, topography of the floor and food can affect the contamination of food.

So I think if you want to keep healthy, you’d better not believe three-second rule and five-second rule.

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