The five-second rule is one of the most cherished bits of household nonsense: A piece of food that has been dropped on the floor can safely be eaten if it is picked up within five seconds.
Now, researchers in England claim there may be some scientific truth to it.
A team of biology students at Aston University in Birmingham, led by microbiology professor Anthony Hilton, conducted experiments on common foods dropped on common floor surfaces. Toast, pasta, cookies and sticky candy were all dropped on floors with carpet, laminate and tile surfaces. The floors had been coated with Escherichia coli (E. coli) and Staphylococcus aureus.
The researchers monitored how much of the bacteria were transferred from the floors to the food items in periods ranging from three to 30 seconds.
The researchers found that the longer the food stayed on the floor, the more bacteria it picked up. The type of surface it landed on also made a difference. Food dropped on laminate and tile floors was much more likely to get you sick than food that lands on carpet.
“I always live by the rule,” said Donna M. Duberg, assistant professor of clinical laboratory science at St. Louis University. “I do try to get people not to be paranoid.”
Whether you should eat food that has landed on the floor depends partly on how clean the floor is, she said. If it is free from dust and dirt, “that’s a definite plus.”
“If you wear your shoes outside of your house, most shoes that you wear within three months will have E. coli on their soles. If you do wear your shoes inside the house, that can bring in a significant amount of E. coli on your floors,” she said.
What you drop is also important. A piece of toast that lands butter-side-down is far more likely to pick up bacteria than one that lands on the bread side, Duberg said. And you should also take into account your own health.
“If you’re healthy, we take in a lot of bacteria every day and our bodies are able to handle that. But if you start getting ill, like with colds or the flu, or if your immune system is compromised or if you are a transplant patient, you shouldn’t eat it,” she said.
“If you’re healthy, go ahead and eat it. Especially if it’s chocolate.”
Daniel Neman is a food writer. Follow him on Twitter @DNemanFood