5-Second Rule: Fact or Fiction? A study finds it’s safe to eat food dropped on a floor, even in the employee lunchroom. Hear from the scientist who conducted it.
Prof. Anthony Hilton, head of Biology and Biomedical Sciences at Aston University, Birmingham, England, reveals the results of his microbiology study in this podcast
Prof. Hilton’s students tested microbial survival on indoor flooring surfaces, and found it is safe to eat food dropped on a floor which is cleaned on a regular basis. The study is not about food dropped outside in dirt near a campfire. Prof. Hilton makes it clear in this interview that the study only included food dropped on indoor surfaces, including vinyl and carpet.
Dan Clark conducts this interview with the sometimes serious, sometimes funny Prof. Hilton. Scroll down for the study. It’s linked in the transcript.
Brandon Nys: Welcome to Safety Experts Talk. Visit our website at CreativeSafetySupply.com/podcast for links and transcripts.
Dan Clark: I’ll admit it. I’m guilty of eating food off the floor. And I think I’ve finally been justified. Let’s talk with Prof. Anthony Hilton at Aston University in Birmingham, England. Hi, Professor.
Prof. Anthony Hilton: Hello, and thank you.
Dan: Professor, I’m a typical American male, and I eat food off the floor.
Prof. Hilton: (laughter).
Dan: Please tell us about your study and maybe how it might affect the average worker.
Prof. Hilton: Well, some of the students that I was working with introduced me to this idea of the Five Second Rule which is: if you drop food on the floor that if you pick it up within a period of five seconds then maybe fewer bacteria will have got onto it than if you leave it for longer. What we did is dropped food onto the floor.
Prof. Hilton: We looked at how many organisms had made the transfer from the floor at three seconds, which is under the Five Second Rule, and at 30 seconds, which is obviously after the Five Second Rule.
Dan: Uh-huh. And, what was the result? Did the bacteria pull out stopwatches and respect this Five Second Rule?
Prof. Hilton: Well, the initial impact of the food on the floor does transfer a number of microorganisms. But what we found, which others have not really looked at further, is that the longer that food stays on the floor, the actual more bacteria accumulate.
Dan: In our lunchroom…
Prof. Hilton: Sure.
Dan: The Five Second Rule does not apply to Jell-O or pudding.
Prof. Hilton: (laughs)
Dan: Obviously that’s not what you tested but toast, pasta, biscuits, sticky sweets. Which of those were most likely to collect bacteria?
Prof. Hilton: I’m, I’m entertained and reassured by your clarification of how you apply the Five Second Rule, which is fantastic.
Prof. Hilton: We tried to model the entire process from a bacterium being on the floor, using your food as a vehicle, and then ultimately arriving in your mouth and therefore causing an infection. And we wanted to look at that chain of events and what was happening.
I think it would help your listeners if I just explained that, in addition to the laboratory studies that we undertook, we also surveyed indoor flooring. And I think this is important, because some of the people I’ve spoken to say “Well, you know, what about if I drop some food on the sidewalk or down the Underground or whatever, down the tube station?” And that’s outside, and that’s a whole different environment. And we’re not really talking about that at all. We’re talking about indoor environments where there’s some element of cleaning. Some element of, maybe, brushing up dust and crumbs. And, maybe, some element of mopping with a biocide once a week, or whatever, such as you might employ in your own home, or your employer might do in your own cafe.
So those types of indoor floors, they contain a very low number of microorganisms. And that’s what we found repeatedly. We surveyed lots of indoor environments, both carpet, and tiled and laminate floor. And we found very few bacteria there. And the ones that we did find, were normally those that we might find on the skin.
My interpretation of this is that you’re at no greater risk of shoving your fingers in your mouth than you are of dropping food on the floor in that regard, because the organisms that we find are the same. They’re the same staphylococci. Organisms that we see on the skin are the ones that we find the floor. And it’s a recognized contribution to indoor microbiology that humans are the biggest source of microbes in the indoor environment.
If we then drop some food on that floor, what we found is that the transfer rate—the transfer efficiency—was a millionth of what was there. So that means if there were a million bacteria on that particular piece of floor where you drop your food, a millionth would transfer, which is one. So, one in every million get transferred.
Now, the infectious dose of many microorganisms, which is the number of organisms we need to consume to make us unwell, is quite high. It could be in the tens of thousands, in the hundreds of thousands. And we just don’t see that level of transfer.
I, kind of, approach this as a quantitative risk assessment by asking the question “What is on the floor, and how many are there? What is the transfer efficiency if I drop a particular piece of food on the floor and how likely am I to consume a number of organisms that will make me unwell?” And in none of our experiments did we ever get anywhere near the number of organisms we’d need to make us unwell.
Dan: Wow. That is amazing. So, you, Prof. Hilton, head of Biology and Biomedical Sciences at Aston University, Birmingham, England, say that it is okay to eat food that’s fallen on the floor.
Prof. Hilton: Well, it’s difficult to give you a yes or no answer to that. But, what I can say is that within certain caveats, because, obviously, there’s extremes of data. If you drop a food directly onto a colony of harmful bacteria and they just happened to transfer and you just happened to eat it, then of course you’re going to be ill. And it would be wrong of me to say that there’s no risk.
But we have to look at what usually happens and in our experiments, a typical indoor environment has very few bacteria on the floor that would make you unwell. In our experiments the food we dropped on the floor typically transferred a fraction of the organisms that were there, and so those losses at each stage in the process means that the likelihood of you actually consuming food that will make you unwell is very low.
And that is our interpretation. Of course, we can’t say every case but in our experiments it would seem to be very low.
Dan: Your survey seems to flesh that out a little bit in that a vast majority say they either have, or wouldn’t have a problem with, eating food off the floor. Is that true?
Prof. Hilton: That’s…yeah. That’s a really interesting observation because in modeling this idea, we came up with the idea that if nobody ever ate food that dropped on the floor, then it didn’t really matter whether bacteria transferred or not, because there would never be that final link in the chain taking contaminated food into somebody’s mouth.
And so we did a survey of…they were largely students. And I don’t know what students are like in the states compared to the UK students, but they tend to have a reputation that they were probably more likely. They don’t have much money, and they, sort of, may struggle to find fresh food if they dropped it on the floor. And so, to be honest with you, we thought they’d be more likely to do it. But we also coupled that with a Facebook study as well which included other people which weren’t students and older people and younger people and all the rest of it.
And this was purely based on the UK data. We found of the 495 people that we surveyed, 87% of them said they would eat food that dropped on the floor which is more than I had anticipated.
Dan: Well, it surprises me also that the majority of those were women.
Prof. Hilton: Absolutely. Well, other people have found this. There was a story, which, I believe, came out of Harvard, or one of the certainly reputable institutions in the states, where, I think the researcher’s name was Clarke, who was awarded the Ig Nobel Prize for this work. And as part of their work, they looked at the Five Second Rule. And they also found that females were more likely to consume food having been dropped on the floor than males, which I suppose we could be accused of being socially, kind of, biased. But you get the impression, certainly in the UK, that females will be less likely to do that because they are more aware in other studies.
For example, we did a survey “Would male or females be more likely to consume food that had passed its ‘Use By’ date?” In all those studies, it’s always males. Males are far more maverick about those things. We asked males and females “Who will be more likely to eat foods that they believe to be undercooked?” So, this might a burger or some meat that had been consumed. And males, always, they’re far more bravado about those things.
So we, kind of, assumed in this circumstance that it would be the same. But we actually found different. But that’s been supported by others.
Dan: It surprises me too, because women here in the states are most likely to say “Ooh, that’s icky” when they see food that’s dropped on the floor, so, maybe they have a secret life that we don’t know about.
Prof. Hilton: (laughs) I think they all most certainly do.
Dan: I understand that MythBusters, the television show here in the United States, did a similar study about the Five Second Rule. Are you familiar with that study and do you think your study is more complete?
Prof. Hilton: Yes, I am familiar with their study, and what they undertook was to take agar plates—contact plates—and they put them on the floor for three seconds, for example, and they may have put them on the floor for longer than that. And then they tried to compare the numbers between. And, I believe in their investigation, they didn’t find any difference and therefore they suggested that the Five Second Rule was a myth.
To some extent they are right. And it’s, more or less, what we’ve shown as well is that on impact food picks of a set number of organisms. And that’s what they were showing with their, kind of, “early” contact plates. But, what they weren’t really taking account for, and what our study showed, is that with dried foods, like toast and biscuits, time was not a factor at all. We dropped biscuits and toast onto all of our flooring surfaces. The number of organisms we found at three seconds compared to 30 seconds was not significantly different, suggesting that time was not a factor.
However, for moist foods, such as pasta and the sticky candy sweets, that was where time became a factor. And, so, it led us into the observation that it’s the nature of the food and how it contacts with the floor that really dictates whether time is a factor.
You can imagine that on a micro scale that a piece of pasta that has hit the floor has a certain number of contact points between the pasta and the floor which allows microbes to make that transition from the floor onto the food. And then, if it’s left for a period of 30 seconds, the floor, being flexible in its nature, will make additional contact points as it settles onto the floor and therefore allowing additional microbes to make that transition over.
So we’re looking at this from the point of view of the food and not the point of view of the microbes. It’s quirky to think of organisms is being highly motile, with stopwatches, thinking “Right. Time now. We better run and jump on this food.” It doesn’t really work like that, of course.
What it is, is that the food, having a certain amount of fluidity to it, hits the floor. It picks up a certain number of organisms, which we’ll call X. Over 30 seconds, additional contact points are made between the food and the floor which allows additional organisms, which we’ll call Y, to be added. And that’s why the Five Second Rule works because of the nature of the food.
Dan: Okay, good. So, workers are probably safe eating certain foods dropped in the lunch room. Or do you have other advice for them?
Prof. Hilton: Well (laughs) I, I think that you should probably add additional parameters to the Five Second Rule. And my additional parameters would be “How much does the food cost that you dropped?” And “Are you standing in the gent’s toilets at the time?”
Dan: (laughs) Well, our lunchroom and gent’s toilets are separate facilities here and I hope that most of the time they are in other places as well.
Prof. Hilton: Yeah, I agree.
Dan: I understand that there are more microbes in our bodies than actual human cells is that true?
Prof. Hilton: Yes, yes.
Dan: That’s an amazing statistic.
Prof. Hilton: Yeah, it’s…it’s ah…we’re, we’re nothing more than petri dishes with shoes on, really.
Dan: (laughs) Before we go, I do have one last question on the Five Second Rule.
Prof. Hilton: Sure.
Dan: Do you, sir, eat food from the floor?
Prof. Hilton: Yes! (laughs) I do. And, and I, I have three young boys and any parent will know that if you send off a child with a piece of toast within a few seconds it will be on the floor. And there’s only so much toast you can make as a parent, really.
Prof. Hilton: We’re all doing the risk assessment all the time. And, although we have made light of the situation, I think if it’s in your own home where you know when you last cleaned the floor, you have a general idea of the hygiene status of your home, and you drop a piece of toast on the floor, I would pick it up. There’s absolutely limited risk. You’ve more chance of winning the lottery than getting a disease.
Dan: Well, if I were a guest in your home, I think I would do the same.
Prof. Hilton: (laughs) You’re always welcome, anytime.
Dan: Well, thank you very much professor for being part of our podcast today.
Prof. Hilton: It’s been a pleasure. Thank you very much.
Dan: We’ve been speaking with Prof. Anthony Hilton from his office at Aston University in Birmingham, England. He’s their head of Biology and Biomedical Sciences, and his team did the study on the Five Second Rule. The study is posted at our website creativesafetysupply.com/podcast. Just look for the episode titled The Five-Second Rule Is Real. I’m Dan Clark.
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