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Today in the cafeteria my friend dropped a chicken wing on the floor and immediately picked it up and ate it. Afterward he claimed that the chicken wing was still safe to eat if it was consumed within 5 seconds after being on the floor. He said that it's the "five second rule". Is this rule safe to follow?

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    It depends on the floor (if the floor is covered in shit then it's probably not safe, but if the floor is sufficiently clean then it probably is). When I was growing up, picking it off the floor quickly was to get it before the dog did. – ChrisW May 16 '11 at 6:35
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    mythbusters did this one. It was highly entertaining – Monkey Tuesday May 16 '11 at 6:46
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    As Monkey said: Mythbusters tested this and came to the understandable result that the amount of time the foot lies on the ground has no reasonable influence on the amount of bacteria it gets in contact with. In other word: Direct after the food hit the ground it is already "contaminated". Waiting 1, 5 or 10 seconds before picking it up didn't made any real difference. – Martin Scharrer May 16 '11 at 10:09
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    I'm pretty sure the purpose of the 5-second rule is to avoid social- or even self-disapproval for doing the icky thing of eating food off the floor. Assuming a relatively clean floor, it's really not that dangerous. But people think it's gross and it's looked down on. The solution? The 5-second rule, where you can salvage your food while saving face socially. I doubt many people really believe the 5-second rule is a valid means to avoid bacteria, but we all agree to pretend it does in order to not waste food. – Brian Schroth May 16 '11 at 12:56
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    In college it's the "48 hour rule" – Travis Christian May 16 '11 at 18:03
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Jillian Clarke researched this in 2003 when she was a high school science intern at the University of Illinois.

Among Clarke's findings:

  • 70% of women and 56% of men are familiar with the 5-second rule, and most use it to make decisions about tasty treats that slip through their fingers.
  • Women are more likely than men to eat food that's been on the floor.
  • Cookies and candy are much more likely to be picked up and eaten than cauliflower or broccoli.
  • And, if you drop your food on a floor that does contain microorganisms, the food can be contaminated in 5 seconds or less.

Clarke was awarded the 2004 IG Nobel Prize in Public Health for her work.



Food Scientist Paul Dawson at Clemson University also looked into it.
His findings were published in the Journal of Applied Microbiology:

Three experiments were conducted to determine the survival and transfer of Salmonella Typhimurium from wood, tile or carpet to bologna (sausage) and bread.

In the case of the 5-second-rule we found that bacteria was transferred from tabletops and floors to the food within five seconds, that is the 5-second-rule is not an accurate guide when it comes to eating food that has fallen on the floor.



The MythBusters also busted the 5-second-rule:

Even if something spends a mere millisecond on the floor, it attracts bacteria. How dirty it gets depends on the food's moisture, surface geometry and floor condition — not time.

Here is the video.

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    +1 - Fantastic, comprehensive answer. A worthy field of study for an Ig Nobel Prize too. :) – user2466 May 16 '11 at 11:45
  • lol @ Nobel Prize for this. – Kevin Peno May 16 '11 at 17:26
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    @Kevin: The IG Nobel Prize is a negative prize and to the real Nobel Prize like the Golden Raspberry to the Oscar. – Martin Scharrer May 16 '11 at 19:07
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    +1 For finding an Ig laureate in the field (and for being the image master). – Rusty May 16 '11 at 22:48
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    @Martin IG Nobel is not at all a negative prize. – Stefan Aug 28 '12 at 16:15
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While perhaps not a real answer for the question, I would like to highlight some grass roots skepticism that a question such as this can be the basis for. An actual scientific study on this phenomenon/saying was conducted by a High School senior. See, ANYONE can do real science, and it may even prove interesting to folks.

Yes, someone really has conducted a scientific study of the five-second rule. It was the project of high school senior Jillian Clarke during a six-week internship in the food science and nutrition department at the University of Illinois at Urbana-Champaign. Meredith Agle, then a doctoral candidate, supervised the study.

"Jillian swabbed the floors around the University in the lab, hall, dormitory, and cafeteria to see how many organisms we could isolate," Agle tells WebMD. "We examined the swabs, and there were very few microorganisms. That surprised me. I told her to do it again."

The results were the same. Agle has since earned her doctoral degree and is a scientist in new product development for Rich Foods in Buffalo, N.Y. "I think the floors were so clean, from a microbiological point of view, because floors are dry, and most pathogens — like salmonella, listeria, or E. coli — can't survive without moisture."

Just remember, if it's cake on the floor, it's a lie!

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http://www.boston.com/business/ticker/2007/05/5second_dropped.html

it is, in fact, 30 seconds for wet food, or much longer for dry food, according to this study

We're looking for long answers that provide some explanation and context. Don't just give a one-line answer; explain why your answer is right, ideally with citations. Answers that don't include explanations may be removed.

  • The other study, whose results differ from the one you reference, seems a bit sounder methodologically – Lagerbaer May 17 '11 at 0:20
  • Here is the original article, and here is an ABC News Video. It seems like the methodology is the same: drop food, wait various times, swab the food, cultivate bacteria. – Oliver_C May 17 '11 at 0:29
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    Please expand this in a full answer. Link to the studies, provide citations, &c. Are the studies reliable, yes? no? – Sklivvz Aug 25 '12 at 11:33

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