Testing the Five-Second Rule

You’ve just opened a new package of candy and you accidentally drop a piece on the floor. “Five-second rule!” your friend shouts. You quickly pick up the candy and pop it into your mouth. The “rule” says that if you pick up fallen food within five seconds, there’s no time for germs to climb aboard—right? Not so fast.

Most scientists have long believed that the five-second rule is a myth. But researchers at Rutgers University in New Jersey wanted to back up that belief with data. They designed an experiment to test if there’s any truth to the popular rule.

You’ve just opened a package of candy. Oops, you drop a piece on the floor. Your friend shouts, “Five-second rule!” You grab the candy. You pop it into your mouth. The “rule” says there’s no time for germs to climb onto fallen food if it’s picked up within five seconds. Sounds right? Not so fast.

Most scientists have long believed that the rule isn’t true. But scientists at Rutgers University in New Jersey wanted to back up that belief. They needed data. So they decided to test if there’s any truth to the popular rule.

The scientists decided to test the five-second rule using watermelon, gummy candy, plain bread, and buttered bread. They chose those foods because each contains a different amount of moisture. “We know water is very important in allowing disease-causing bacteria to transfer,” says Donald Schaffner. He’s the food scientist at Rutgers who led the study. 

Next, Schaffner’s team picked four common household surfaces to drop the foods on: tile, stainless steel, wood, and carpet. They spread millions of bacteria onto each test surface. 

The final variable, or factor the scientists changed in the experiment, was time. They left the foods on each surface for less than 1 second, for 5 seconds, for 30 seconds, and for 300 seconds. 

To make sure their results were reliable, the scientists tried each combination many times. After each trial, they tested the foods to see how much bacteria they had picked up. Would the five-second rule work?

The scientists used different foods in their experiment. They chose watermelon, gummy candy, plain bread, and buttered bread. They picked those foods for a reason. Each has a different amount of water. “We know water is very important in allowing disease-causing bacteria to transfer,” says Donald Schaffner. He’s a food scientist at Rutgers. He led the study. 

Next, Schaffner’s team picked four common surfaces. They chose tile, stainless steel, wood, and carpet. They spread millions of bacteria onto each test surface. Then they dropped the foods onto them. 

The final variable, or factor scientists change in an experiment, was time. They left the foods on each surface for less than 1 second, for 5 seconds, for 30 seconds, and for 300 seconds. 

The scientists tried each variable many times. They wanted to make sure their results could be trusted. They tested the foods after each trial. They wanted to see how much bacteria they had picked up. Would the five-second rule work?

In most cases, the scientists found, food did pick up more bacteria the longer it sat on a surface. But that wasn’t the only important variable. The food’s moisture level and the type of surface it fell on also made a difference. Juicy watermelon picked up more bacteria than gummy candy, for example. And carpet transferred fewer germs than hard surfaces like tile.

In every test, though, at least some bacteria got on the food—even when it was picked up immediately. That means the five-second rule is a bust, says Schaffner. “There was no safe amount of time,” he explains. 

So should you eat that dropped piece of candy? Probably not, scientists say. According to the Centers for Disease Control and Prevention, germy surfaces are to blame for 12 percent of food poisoning cases. No matter how good that fallen food looks, the safe choice is to toss it!

The scientists found that food did pick up more bacteria the longer it sat on a surface in most cases. But that wasn’t the only important variable. The food’s wetness also made a difference. So did the type of surface it fell on. Juicy watermelon picked up more bacteria than gummy candy, for example. And fewer germs stuck on foods dropped on carpet than on hard surfaces like tile.

At least some bacteria got on the food in every test, though. Germs stuck to food even when it was picked up right away. That means the five-second rule is a bust, says Schaffner. “There was no safe amount of time,” he explains. 

So should you eat that dropped piece of candy? Probably not, scientists say. Germy surfaces are to blame for 12 percent of food poisoning cases. That’s according to the Centers for Disease Control and Prevention. No matter how good that fallen food looks, the safe choice is to toss it!