The Five Second Rule Works Best on Carpet
The “five second rule” is an unofficial pass to eat food dropped on the floor—provided only a few seconds have elapsed. The general wisdom is that it takes several seconds for bacteria to transfer to the food item, making it safe to eat if picked up quickly. In one survey, 87% of people admitted to eating dropped food at least once. The five second rule was never backed up by science but some researchers have decided to test the idea.
In the first major study, researchers tracked the transfer of common bacteria, including E.coli, to food after it had been dropped. They found that carpet was less likely to transfer bacteria than smooth surfaces. While moist foods could become colonized within seconds, most foods were declared safe. For dry snacks, such as cookies, it could take 30 seconds or longer for bacteria to show up. The researchers decided that the five second rule works—in specific cases.
This year, however, a different team of researchers decided to investigate the rule. The new study was larger and included a greater variety of foods. Once again, the team found that carpet was the “safest” and was slow to transfer bacteria. The one exception was sticky foods but those foods tended to absorb bacteria within seconds no matter where they were dropped. It could take a while for bacteria to transfer to dry foods but wet foods, such as watermelon, were colonized almost immediately. Generally, even in the safest scenarios, some bacteria ended up on the food item. The team concluded that the five second rule is risky. There are a lot of variables involved (wood floors, for example, were inconsistent in the amount of bacteria transferred) and in most cases, the food ended up contaminated quickly.
The takeaway? The five second rule isn’t based on any actual science. Contamination rates instead depend on the type of food and the floor surface. Sticky foods should never be eaten when dropped while dry foods may be safe, especially if dropped on carpet. In the end, people should do whatever they’re comfortable with—just know that the “rule” won’t necessarily save you from food poisoning.
photo: Travis Wise