You’re eating a particularly tasty snack when, oops, you drop it on the floor. The item is solid, like a cookie, and not liquid-y or gooey, ice cream. The floor is reasonably clean, at least to the naked eye. You have a relatively strong immune system, just in case, and, uh, no one is looking. So you quickly check to make sure the food item hasn’t been on the floor for too long, scoop it up, and eat it. “Too long,” of course, is governed by the old guideline known as the “five-second rule” — you have five seconds to pick up that cookie before it’s no longer safe to eat.
That rule isn’t steeped in decades of scientific research, of course; its origins are unknown, but it is unlikely that the first people to adopt the rule did so only after a series of double-blind tests in laboratory conditions. That’s the bad news. The good news?
The five-second rule may actually be, roughly speaking, valid. Scientifically.
A team of researchers from Aston University in Birmingham, England, issued a paper last month testing the five-second rule-of-thumb. (It’s not been published in a journal nor peer reviewed.) As TIME explained, “To test out the rule, students dropped toast, pasta, biscuits [cookies, for us Americans], and candy onto a floor that had been exposed to common bacteria and measured how much of the bacteria transferred when it was left on the surface for durations ranging from three to 30 seconds.” The common bacteria? Escherichia coli (E. coli) and Staphylococcus aureus, neither of which are really fun to have inside your digestive system, and best avoided.
What they found? Well, five seconds isn’t a precise rule — it’s more of a range. The research team discovered that the type of flooring the food lands on is of critical importance as it is a significant factor in the rate of floor to food bacterial transfer. The Aston summary notes that bacteria are “most likely to transfer from laminate or tiled surfaces to moist foods making contact for more than 5 seconds.” On the other hand, it is a much better idea to consume that same snickerdoodle or piece of toast if it landed on carpet — sure, you may get a little fuzz stuck to the snack, but the bacteria doesn’t come over as readily. The five-second rule, strictly applied, is something that applies to food dropped on tiles/laminate — carpet-landings may provide for a longer window, they discovered.
But that doesn’t mean you should take that risk — regardless of food type or flooring material. In a video hosted by Smithsonian.com (via this Slate article), another professor asserts that eating food that has hit the floor is like “playing Russian roulette with your gut.” That’s probably not a great idea, but if you’re one who takes that risk, rest assured you’re not alone. Aston University’s research found that 87% of people surveyed admitted to eating food they’ve dropped on the floor.
From the Archives: Where No Sandwich Has Gone Before: Food which went up, not down.
Related: 5 Second Rule, a board game with a lot of very positive reviews, but sadly, no cookies.