A Rule Without a Clear Origin
The so-called “five-second rule” suggests that food dropped on the ground is safe to eat if picked up quickly—typically within five seconds.
The phrase appeared in modern print in 1995, but some trace its origins to a myth about Genghis Khan, who reportedly believed food could remain on the ground “as long as Khan allowed,” under the assumption that food made for him remained worthy regardless of where it landed. However, no direct historical source confirms the tale.
The First Scientific Look
In 2003, high school student Jillian Clarke investigated the rule during an internship at the University of Illinois. She surveyed participants and found that the majority were familiar with the rule.
Clarke tested bacteria transfer using E. coli on tiles and discovered that food could pick up bacteria even after brief contact. For this study, she received the 2004 Ig Nobel Prize in public health. She also found that public flooring was surprisingly free of harmful bacteria in her samples.
Surfaces and Bacteria Behavior
In 2007, researchers tested how salmonella transferred from wood, tile, and carpet. Bacteria were able to survive on dry surfaces for nearly a month. In tests, food items like bread and lunchmeat picked up salmonella in under five seconds. However, longer exposure increased contamination rates significantly, especially on tile and carpet.
Further Evidence From Rutgers
In 2016, scientists at Rutgers University examined food items dropped onto carpet, wood, steel, and tile. The foods included watermelon, gummy candy, white bread, and buttered bread. The bacteria used was Enterobacter aerogenes.
Results showed that moist foods, like watermelon, attracted the most bacteria and that surface type played a critical role. Surprisingly, carpet transferred fewer bacteria than tile or stainless steel. Researcher Donald Schaffner concluded: “Bacteria can contaminate instantaneously.”
Disagreement and Variability
A 2014 study by students at Aston University in the UK suggested some validity to the five-second rule, showing that foods picked up quickly may carry fewer bacteria.
Microbiology head Anthony Hilton later noted in 2017 that while some floor exposure might carry little risk, especially for dry food, contamination increased substantially after 30 seconds.
Popular Media Take
The rule was tested on shows like MythBusters and Food Detectives, both of which found that contamination happens immediately and is influenced more by moisture and surface type than by time alone.
Conclusion
Scientific consensus finds that bacteria can transfer to food instantly and that the five-second rule oversimplifies the risk. Variables such as food moisture, surface cleanliness, and contact duration all affect the degree of contamination.
The five-second rule says dropped food is still safe if you pick it up fast enough.
It's been passed around kitchens, schools, and picnics for years. But is it really true?
Scientists have put this belief to the test across decades, and the results may surprise you…🧵👇 pic.twitter.com/EOvg2pHFj3
— Detective Tiger's Stories (@TigerDetective) July 2, 2025