When you're saving the best bite for last and it drops on the floor, the instinct is to pick it up - but would you eat it?
Researchers from the United Kingdom's Aston University surveyed 495 people in 2014 about the five-second rule - the belief that picking up dropped food within that timeframe would mean it is still okay to eat. They found 87 percent said they would eat or have eaten spilled food.
Unless you are living in a sterile environment (which is pretty much impossible), there is no doubt dropped food picks up some germs, as 2007 research by US Clemson University food scientist Dr Paul Dawson shows.
Clemson University food scientist Paul Dawson. Photo: Supplied / Clemson University
Another study in 2016 by America's Rutgers University found time was a factor in how much bacteria got onto the food, but the food's moisture and the type of surface it was dropped on were more relevant when assessing contamination.
"There's no easy answer," Dawson told RNZ's Afternoons. "There are some differences due to the surface, due to the food, time does make a difference in number [of bacteria], but from a practical standpoint - even if it's a different surface, different food - if there's harmful bacteria there [on the surface], it's going to be picked up immediately. That's kind of the take-home common-sense method."
The Ministry for Primary Industries says the 'rule' is a myth. While its scientists agree the moisture and stickiness of the dropped food will affect how many germs latch on to it, their advice is that it is better to bin it than stick it back in your mouth.
Photo: RNZ
So will I get sick if I eat dropped food? What are the risks?
Dr Dawson says the statistical odds of a pathogen residing on that one spot you dropped something could be low. However, he would never advise anyone to eat dropped food on the basis that there is still a risk - and it is better to be safe than sorry.
"If you happen to be in a location like the kitchen where there's been raw food handled [or] in a hospital - places like that would be high risk."
Another risk factor would be your immunity - those who are immunocompromised, have not yet developed their gut flora, or are elderly could be more susceptible to illness from exposure to even a low amount of bad bacteria compared to a healthy person, he says.
"From a food safety standpoint, if you have millions or more cells on a surface, 0.1 percent is still enough to make you sick. Also, certain types of bacteria are extremely virulent, and it takes only a small amount to make you sick," Dawson wrote in 2022 for The Conversation.
University of Otago Senior Teaching Fellow Judith Bateup. Photo: Supplied / University of Otago
University of Otago senior teaching fellow Judith Bateup, who has researched the microbiology of the gastrointestinal tract, has also rubbished the five- or six-second rule, saying contamination is instant.
If you choose to eat dropped food, you should consider what pathogens that surface may have been exposed to, she says. For example, have you had animals wandering across the floor, or do you wear shoes inside your house?
But we also need to remember that nothing is completely germ-free; microbes are in, on and around us all the time.
"We have 10 times more microbial cells in our body numerically than we have human cells. So again, it shows how important the good bacteria are to us."
Additionally, stomach acid kills most bacteria as food gets digested and immune cells can deal with pathogens before we physically sense anything, Bateup says.
Photo: RNZ
How does the type of surface and food matter?
Rutgers researchers found watermelon had the most bacteria after being dropped onto surfaces compared to the other foods they tested including strawberry gummies, plain white bread and buttered bread. The result could be explained by the fact that bacteria moves with moisture.
Dawson notes that tabletops may be just as concerning as the floor because they are often where raw food is handled and hands (which often touch tables) are carriers of bacteria too.
His study also found the longer researchers waited before dropping food on inoculated surfaces, the less transfer of bacteria there was as it became more resistant to being pulled off. It also tends to die off if there is no source of nutrients, he says.
Can't I just wash it?
Dawson says you can remove some of the germs by washing your food - but obviously some foods cannot tolerate being washed, so use your common sense.
MPI agrees washing is an option in desperate times for food that can be salvaged (not spilt milk and broken egg) but you'd still want to cook off "the nasties".
So where did the 'rule' come from?
No one is actually too sure, Dawson says. He points to some urban legends as the possible source, including stories of Mongolian empire leader Genghis Khan reportedly having a rule at banquets that food prepared for him could still be eaten if it dropped, as long as he allowed it.
There is also the story of US TV personality and chef Julia Child dropping a pancake on the stovetop and picking it back up, saying: "You can always pick it up if you're alone in the kitchen. Who is going to see?"
Sign up for Ngā Pitopito Kōrero, a daily newsletter curated by our editors and delivered straight to your inbox every weekday.
