According to the so-called five-second rule, it’s safe to eat food after it’s dropped on the floor – as long as you do so within the allotted time frame. It’s one of those “rules” that has stood the test of time, as evidenced by its unwavering presence in everyday culture. In fact, you’ve probably seen plenty of people swearing by this rule. But is it true? Here’s what you should know about the five-second rule for eating, according to a food scientist.

The origin of the 5-second rule

First, it might be helpful to understand how the five-second rule came about. According to Paul Dawson – a food scientist, professor at Clemson University and co-author of Did you just eat that?— the rule comes largely from urban legend. One such story dates back to Genghis Khan, the founder of the Mongol Empire. Khan supposedly established the “Khan Rule” at banquets: if food fell on the floor, it was allowed to stay there as long as he allowed. Several centuries later, chef and television personality Julia Child may have further contributed to the myth. In an episode of the television series “The 1960s” The French chefChild flipped a pancake, which ended up on the stove. She then put the pancake back in the pan, noting that you can always pick it up if you’re alone in the kitchen, Dawson says.

While these stories don’t explain why five seconds became the magic number, they do provide insight into how people learned to deal with dropped food. But does five seconds really make a difference when it comes to safety and the risk of germs?

Ultimately, the 5-second rule is a myth

Unfortunately, there is no truth to the five-second rule. According to Dawson, the level of contamination when food falls on the floor (or any other surface) is determined primarily by the “dirtiness” of the floor, not the duration of contact. In other words, food that falls on a germ-contaminated floor picks up germs, regardless of how long it stays there. Dawson even tested the five-second rule in a laboratory. To do this, he and his team contaminated tiles, wood and carpet with Salmonella Bacteria, one of the most common causes of food poisoning. Next, they dropped sausage (wet food) and white bread (dry food) onto the surfaces and then waited five, 30 and 60 seconds.

The team then measured the bacteria on each food item for each time period. Dawson says high levels of bacteria were found on both the sausage and white bread, regardless of the surface and contact time. And while there were some differences (such as fewer bacteria on dry foods or foods that touched the carpet), there was still a notable level of contamination overall.

Conclusion: When food falls on a surface, it picks up germs. Whether this happens and ultimately increases the risk of food poisoning has nothing to do with how long it falls on the surface.

Is it safe to eat food that has fallen on the floor?

Although the five-second rule is a myth, it doesn’t necessarily mean that food that has been dropped on the floor is no longer safe. The health risk of eating these foods depends on many factors, according to Dawson. These include the amount and type of microorganisms on the surface and the characteristics of the contact between the food and the surface. (After all, bacteria can multiply in certain environments.) It also depends on the general health of the person eating the food. In general, if your immune system is weakened, you’re at a higher risk of getting food poisoning after eating contaminated food.

Washing food can also remove some bacteria, says Dawson. However, “the surface properties of the food would play a role, as some foods don’t wash as well as others,” he says. Cherries or carrots, for example, are easy to wash, but crackers or chicken wings are not.

Regardless of whether food has touched the floor for five seconds or five minutes, it is best to throw it away for food safety reasons.