The 5-second rule: scientists explain how quickly bacteria "attack" food that has fallen on the floor

The good old five-second rule goes like this: if food that accidentally falls on the floor is picked up within this short period of time, it does not have time to become contaminated with bacteria. This statement has always been the subject of both domestic disputes and countless scientific projects.

Some say the rule exists, while others have called it nonsense. Fortunately, modern researchers are finally unraveling the nuances behind the five-second rule, National Geographic writes.

How fast can bacteria settle on food?

The key to the five-second rule is to understand how quickly bacteria are transferred from the floor surface to the food. Many people get this measurement wrong, food scientist Donald Schaffner of Rutgers University says. Amateur scientific studies and television "investigations" have confused the issue by relying on experiments that are not scientifically validated.

In fact, until 2016, there was only one thorough justification for the five-second rule: a peer-reviewed study by Paul Dawson, a nutritionist at Clemson University, in 2007. Dawson and his colleagues reported that food can pick up bacteria immediately after contact with a surface, but this study focused more on how long bacteria can survive on surfaces to contaminate food.

That's why Schaffner and his student Robin Miranda decided to test more different products under more varied conditions. The experiments, which they reported in the journal Applied and Environmental Microbiology in 2016, showed that the five-second rule is not a rule at all.

They found that the longer the food lies on a surface covered with bacteria, the more bacteria sticks to it. But a large number of microorganisms are picked up as soon as the food falls to the ground.

But it's not time that's to blame, it's another factor. Wet foods (such as watermelon) absorb more bacteria than dry foods such as bread or chewing candy. Carpeting has fewer pests than tile or stainless steel because it has absorbed the bacterial solution that scientists used.

Since then, new research has confirmed how easy it is to transfer bacteria in the kitchen, whether on your fingers or simply by using the same board to cut meat and vegetables (even if it is washed between uses).

And in 2021, scientists in Indonesia were inspired to disprove the five-second rule and its Indonesian counterpart, known as belum lima menit, or the five-minute rule.

But is it safe to eat food from the ground?

If science has so thoroughly debunked the five-second rule, does this mean that eating food that has fallen to the floor is dangerous? It depends on the surface and what bacteria you might pick up.

"If you're in the hospital and you drop something, you probably don't want to eat it. Likewise, you definitely don't want to catch salmonella from a kitchen floor covered in chicken juice," Dawson says.

But in most cases, eating a cookie that has picked up some dust and bacteria from the floor is unlikely to harm you if you have a healthy immune system.

"Ninety-nine percent of the time, it's probably safe. Good sanitation, keeping floors and surfaces clean are the most important factors," he says.

The five-second rule is likely to remain popular.

"People really want it to be true. Everybody does it, we all eat food off the floor," Schaffner says.

Perhaps the value of the five-second rule (or the three-second rule, if you're more scrupulous) lies more in the realm of psychology than microbiology. At the very least, having a rule provides a socially acceptable excuse for our unattractive behavior. Just shout out "Five second rule!" before picking up a cookie from the floor and putting it in your mouth, and everyone can have a good laugh.

And that leaves us with one more way to decide whether to eat the candy you dropped: just look to see if anyone is looking.

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