The Truth About the Five-Second Rule for Food: Here's What Science Says About the Popular Maxim

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According to the so-called five-second rule, it's safe to eat food after it's dropped on the floor—at least as long as you do so within five seconds. It's one of those "rules" that has stood the test of time, as proven by its steadfast presence in everyday culture. In fact, you've probably seen your fair share of people swear by the rule. But is it real? Here's what you should know about the five-second rule for food, according to experts and science.

Related: How Long Can You Safely Store Leftovers For?

The Origin of the Five-Second Rule

First, it might help to understand how the five-second rule came to be. According to Paul Dawson—who is a food scientist, professor at Clemson University, and co-author of Did You Just Eat That?—the rule mostly stems from urban legends. One such story can be traced back to Genghis Khan, founder of the Mongol Empire. Allegedly, Khan established the "Khan Rule" at banquets: If food dropped on the floor, it could stay there as long as he permitted. Several centuries later, chef and television personality Julia Child may have further contributed to the myth. In a 1960s episode of The French Chef, Child flipped a pancake only to have it land on the stovetop. She then returned the pancake to the pan, noting that you can always pick it up if you're alone in the kitchen, says Dawson.

Although these stories don't explain why five seconds became the magic number, they do shed light on how people may have learned to handle dropped food. But when it comes to safety and the risk of germs, does five seconds actually make a difference?

Ultimately, the Five-Second Rule Is a Myth

Unfortunately, there's no truth to the five-second rule. According to Dawson, when food falls on the floor (or any surface, for that matter), its level of contamination is mainly determined by the "dirtiness" of the floor, rather than the length of contact. In other words, food that falls on a germ-ridden floor will pick up germs, regardless of how long it stays there. Dawson has even tested the five-second rule in a lab. To do this, he and his team contaminated tile, wood, and carpet with Salmonella bacteria, one of the most common causes of food poisoning. Next, they dropped bologna (moist food) and white bread (dry food) onto the surfaces, then waited for five, 30, and 60 seconds. The team then measured the number of bacteria on each food for each time frame. According to Dawson, high levels of bacteria were found on both the bologna and white bread, regardless of the surface and contact time. And while there were some differences (like less bacteria on dry foods or foods that touched the carpet, for example), there was still a noteworthy degree of contamination across the board.

Bottom line: If food drops onto a surface, it will pick up germs from said surface. The length of contact time doesn't influence whether or not this happens, and ultimately, the risk of food poisoning.

Is It Safe to Eat Food That Has Dropped on the Floor?

Although the five-second rule is a myth, it doesn't necessarily mean that food is unsafe after it's fallen on the floor. The health risk of eating the food depends on many factors, according to Dawson. This includes the amount and type of microorganisms on the surface, as well as the characteristics of the food-to-surface contact. (Certain environments, after all, can make some bacteria flourish.) It also depends on the overall health status of the person eating the food. In general, if your immune system is compromised, you'll have a higher risk of developing food poisoning after eating contaminated food.

It's also possible to remove some bacteria by washing the food, says Dawson. However, "the surface properties of the food would be a factor, [as] some foods would not lend themselves to being washed as well as others," he explains. For example, it's easy to wash something like a cherry or carrot, but not so much a cracker or chicken wing.

So, whether food has touched the floor for five seconds or five minutes, your best bet is to toss it in the name of food safety.