Controversy Over the '5-Second Rule' for Food Dropped on the Floor... US NASA Also Involved [News Terminology]

99% of Bacteria Instantly Swarm Food "Don't Eat"
NASA: Bacteria Move Slower Than Snails "Just Pick Up Quickly"
Partly True... Depends on Floor Humidity and Material

Is the 'Five-second Rule,' which claims that quickly picking up food dropped on the floor within five seconds poses no significant hygiene risk, trustworthy? The debate among scientists continues.

The first proof was attempted not by a scientist but by a high school student. In 2003, Jillian Clarke, a senior at the Agricultural Science High School in Chicago, USA, conducted an experiment dropping gummy bears and cookies on smooth and rough tiles. She discovered that more bacteria transferred within five seconds on smooth tiles than on rough tiles, and more bacteria transferred to gummy bears than to cookies. Her ingenious and unique experiment earned her the Ig Nobel Prize in 2004.

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In 2007, Professor Paul Dawson's team at Clemson University in South Carolina, USA, published related research in the British scientific journal 'Journal of Applied Microbiology.' Dawson's team experimented with how quickly bacteria from the floor transferred to dry food (bread) or moist food (bologna sausage). The results showed that the longer the food stayed on the floor, the more bacteria transferred, and moist sausage transferred more bacteria than dry bread.

Does the Five-second Rule Apply to Food Dropped on Carpet?

When food is dropped on a tile surface, 99% of the bacteria residing there instantly swarm onto the food and form colonies. Depending on the weather, about 50% of bacteria gather on wooden floors to form colonies, but on carpeted floors, less than 0.5% of bacterial colonies transfer to food picked up within five seconds.

Therefore, it was argued that the Five-second Rule applies to food dropped on carpet but not to other floor types. They also found that on dry tile floors, enough bacteria survive to contaminate dropped food even after four weeks.

In 2016, Professor Donald Schaffner, a food scientist at Rutgers University, USA, and his student Robin Miranda discovered that while more bacteria adhere the longer food remains on a bacteria-covered surface, a sufficient amount of bacteria already attach the moment the food touches the floor.

Schaffner and Miranda revealed that moisture, not time, is the critical factor. Their experiments with various foods confirmed that moist foods attract more bacteria than dry foods. Since carpet absorbs the bacterial solution used in the experiments, it transferred fewer bacteria to the food compared to tiles and other surfaces. This disproved the Five-second Rule.

Most recently, Dr. Sumedh Mujumdar, a British physician, shared his experimental results related to food dropped on the floor via his TikTok. Dr. Mujumdar stated that harmful bacterial colonies such as Salmonella, which can cause food poisoning, and Campylobacter, which causes bacterial enteritis, survive on floors for up to four weeks, and 99% of bacterial colonies transfer immediately upon food contact with the floor, arguing the Five-second Rule is a myth.

"81% Are Willing to Eat Food Picked Up Within 5 Seconds"

On the other hand, Dr. Anthony Hilton's research team at Aston University, UK, discovered in 2014 that the amount of bacteria transferring from the floor surface to dropped food varies depending on the time the food remains on the floor. They emphasized that the longer the time, the more bacteria transfer, so picking up dropped food quickly results in less bacterial contamination.

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The team also revealed that in experiments where participants ate food dropped on the floor, 87% were willing to eat such food, 55% of whom were women, and 81% followed the Five-second Rule, supporting the rule's rationality. Dr. Hilton explained, "In households that clean the floor once a week, it is safe to eat all dropped food. For indoor floors, the likelihood of contamination by bacteria on dropped food is minimal."

NASA scientists Mark Rober and Mike Mitcham appeared on the science channel 'Quick and Curious' on February 4, 2016, defending the Five-second Rule. They stated that bacteria transfer immediately in small amounts to any food dropped on the floor, and food picked up after 30 seconds had ten times more bacteria than food picked up within three seconds.

The bacteria's movement speed averages 0.00045 miles per hour, about 1/67th the speed of a snail, so the faster you pick up dropped food, the less bacterial contamination it has. However, they noted that in high humidity floors, the speed increases, and the contact area varies depending on the floor material, so the Five-second Rule may apply differently depending on floor humidity and material.

Ultimately, the Five-second Rule has been found to be somewhat true. It varies depending on factors such as humidity and material. While the rule is less likely to cause harm in relatively clean environments, many experts still recommend avoiding eating dropped food whenever possible. Perhaps due to this controversy, the 'Five-second Rule' was registered as a neologism in the Oxford English Dictionary at the end of 2014.