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Bologna sandwich

Is this delicious bologna sandwich contaminated with bacteria?

PHOTOGRAPH BY BECKY HALE, NATIONAL GEOGRAPHIC

Sarah Whitman-Salkin

for National Geographic

Published March 15, 2014

Once again, you've dropped your snack. You bend down, snatch it up, and gently blow off any dust—and, you hope, deadly germs. You're about to put it in your mouth because, after all, you've got the "five-second rule" on your side: Food that's been dropped is safe to consume if it's been on the floor for five seconds or less.

But really, should you eat it? Is the piece of toast or the potato chip or the cookie you just rescued from the ground safe to eat, or contaminated by bacteria? Science says ... maybe.

Researchers at Aston University in Birmingham, England, now suggest that the five-second rule is indeed true.

But a 2007 study of the five-second rule from Clemson University in South Carolina argues that there is no safe window for dropped food. Their data points to a "zero-second rule."

Here's the strange thing: Both the Aston study and the Clemson study used nearly identical methods of investigation, and ultimately had the same results—but with staggeringly different conclusions. So is the five-second rule legit or not?

The Science: It's All About Bacteria

When you drop a piece of food on the floor, any bacteria living on the floor will adhere to it. So if you eat the food you've dropped, you're also eating any bacteria the food picked up. Both studies set out to determine how long it takes for bacteria on the floor to stick to food.

The studies tested three different floor surfaces: tile, laminate or wood, and carpet. The Aston study used the bacteria Escherichia coli and Staphylococcus aureus, while the Clemson study used Salmonella typhimurium. Clemson tested only bologna and bread, but the Aston study tested a variety of foods with varying degrees of moisture (a piece of dry toast versus a sticky candy).

The studies agree on several points. When food comes into contact with a contaminated surface, the transfer of bacteria to the food is immediate. And tile, wood, and laminate surfaces transfer much more bacteria than carpeted surfaces. The Aston study found, not surprisingly, that moist foods (cooked pasta or sticky candy) were more likely to pick up bacteria than were drier foods (a cookie or piece of toast).

So Is the Five-Second Rule True?

"It appears that Professor [Anthony] Hilton [who led the Aston study] has substantiated our findings," says Paul Dawson, professor of food, nutrition, and packaging sciences at Clemson University and the scientist behind the 2007 study.

Aston University's Hilton agrees: "Our findings support Professor Dawson's," he says, "in that bacteria are transferred immediately on contact." But, he adds, "the transfer efficacy is extremely low ... hence the five-second rule."

But the two professors disagree as to the degree of contamination.

In Hilton's interpretation, "the initial transfer [of bacteria to food] is insufficient [to contaminate the food]. In our study only one millionth of the bacterial population present on the floor was transferred to the dry food, and approximately 20 times more to the moist. For moist foods, on these flooring types, there is underpinning evidence that fewer bacteria will be transferred to food picked up quickly."

Dawson disagrees. "No matter what the surface or contact time," he says, "enough bacteria was transferred to be detected and to make someone sick."

Would the Scientists Eat It?

Not surprisingly, professors Dawson and Hilton each behave differently when it comes to the five-second rule.

"I compare picking up dropped food and eating it to not wearing a seatbelt," says Dawson. "Someone can drive a lifetime without wearing a seatbelt, never have an accident, and not get injured. Someone can also eat dropped food for a lifetime and never get sick. But in the first case, if you have a serious accident you will probably get hurt. In the second case, if the food you ate was dropped on a surface contaminated with a high concentration of a pathogen, you will probably get sick.

"I still stand by the 'zero-second rule,'" he says. "If I drop food on the floor, I don't see the need to eat it even though the odds are it is perfectly safe."

Hilton, of course, takes the opposite approach: "I have three young boys who have grown up dropping toast on the floor and picking it up again," he says. "In my own home, which I know to be hygienically clean, the risk of them picking anything nasty up with the toast is very, very low." But, he adds, "dropping food on the sidewalk is entirely a different matter."

59 comments
Olitha Gunaratna
Olitha Gunaratna

Probably it doesn't matter for some people. But as a practice I will never eat any food I've dropped on the floor, nor encourage anyone, especially children, irrespective they are mine or not, do so. Whatever scientists say, I think it's not hygienic.

Laura-Jean Slykhuis
Laura-Jean Slykhuis

A small amount of germs from time to time builds antibodies; that's my motto.

Mother always said the problem was that scientists discovered germs before they discovered antibodies! So we get so upset about germs. I do agree that a public place is MUCH more dangerous.

Richard Stiller
Richard Stiller

I've been picking food off the floor quickly since I was a kid and I've lived to be 71 (knock on wood), so I guess it doesn't  make much difference.

Doris Enders
Doris Enders

My first thought was, I want to become a scientist to do studies like this! - Second I think it depends how good the cookie you drop might taste!

Stephen Taylor
Stephen Taylor

Also, I just read a study of the double dip prohibition.  Seems as if the germ transfer from double dippers (ex. person who dips a piece of celery, chomps off the end and dips again) is not enough to be a problem.  I would not be surprised if the next study came to a different conclusion.

Stephen Taylor
Stephen Taylor

I have seen similar studies before.  News from this: the transfer is slow so the number of bacteria transferred can be reduced by a quick pickup.  Previous studies concluded that a sidewalk in the sun was more germ free than the typical home kitchen floor.  I believe that is true.  Second point, I just read that one of the issues with current cleanliness towards food is that we aren't exposed to wide range of bacteria and all those billions of cells in our colons need some new neighbors.  My personal conclusion, I would pick up and eat a whole almond from my floor but not a piece of cake or other soft damp food.

Jane Thompson
Jane Thompson

...oh woes to the kid who eats a cookie off the floor.  Part of the problem with our antibodies/abilities to fight infections are we are TOO clean.  My grandkids come to visit and they play in the dirt with trucks and cars.  How funny, the person who lets their dog lick their face won't eat a cookie from the floor.  And unless you leave your shoes at the front door...

Kirk Out
Kirk Out

Chances are, the hand that holds the cookie has more bacteria than the floor


Emmanuel Owusu
Emmanuel Owusu

oh my God! the kids in the house says the 5 seconds rule... long live our kids!

Kevin Clark
Kevin Clark

The fact of the matter is, the more you subject yourself to bacteria, the stronger your immune system becomes. In other words "What doesn't kill you , makes you stronger"

Gabriela K.
Gabriela K.

Small children constantly eat things they just dropped or which they find on floors. They normally do not get ill. Why is that?

Scott Stewart
Scott Stewart

Have they taken airborne pathogens into consideration? I think it would not matter. if the flu virus got into your system via an oraphis such as an eye or nostril or by picking up a contaminated grape and eating it, either way, you will still become sick. Everything we eat is contaminated. Our bodies "learn" and "remember" how to render these pathogens harmless, so the more we expose ourselves to these, the more "immune" we become to these particular strains through adaptive immunity. 

Mary Gallagher
Mary Gallagher

I would never eat anything off my floors - that's where my cat plants his butt.

Larry Downs
Larry Downs

It seems to me that it is impossible to to substantiate either of the assumptions. The most important factor, in my mind, would be where the floor is located and what kind of traffic it was enduring. Obviously the steps outside a cattle barn or a pig sty might be more likely to contaminate than the floor in your mother's kitchen. Even closer in proximity  the bathroom floor of your home and the kitchen floor of your home. From which would you eat?


Gary Robinette
Gary Robinette

I believe that the time of the rule changes with the type of food being dropped. Lima beans or a radish might be good for up to 5 seconds (or most likely just thrown away) but a piece of chocolate may be good for 30 seconds or more. 

Di Rolands
Di Rolands

I suppose it depends where the floor is and what has been walking on it really , it probably helps your immune system to consume some dirt sometimes .

Douglas Fonacier
Douglas Fonacier

There is no hard and fast rule in this case. It depends on where you drop the food. If near the bathroom, kitchen, garbage area, dirty floor etc., there would be a lot of bacteria there. If on a cleaner surface like table, chair newly-srubbed floor etc. then common sense dictates that there would be lesser amount of bacteria so probably safer to eat.

Bistecca Mammuth
Bistecca Mammuth

I'm sure ! I WAS sure. I believe it ... otherwise the humsan species had been extinguished many many years ago ! ... We have so many good natural defenses (the probe is that we are still a "not extinct species"... ) but ... economy, publicity, big pharmaceutical farms, submitted doctors and stupids ... don't want the people can believe this ! ... :( :( ... Modern society is totally silly ... and happy of it ! ... ^_^ - Oh, I'm a biologist - Massimo P. - Italy

Kai Edwards
Kai Edwards

Think about pre 19th century times when the western world and europe were disgusting.  Bathing was limited, hand washing was typically washing your hands one person after another so only the first person had clean hands.  Who is to say the utensils and serving-ware wasn't disgusting?  It all had bacteria, but everyone was exposed to it, and had enough healthy bacteria to not worry about it.  


Whereas Asian countries have always been finicky about being very clean without being too clean.  They too had few instances of food-born sickness due to their good hygiene.  So, both are true for keeping people healthy.  However, a person with a compromised immune system cannot fight off all the excess from being filthy or dirty.

In the modern world we are overly obsessed with hygiene, and take it too far.  It's to the point where we use sanitizers too often that not only kill off the "bad" germs and bacteria, but also destroy our own, and recent studies have shown that causes our hormones to go out of whack.  Given the lack of bacteria and germs, both good and bad our bodies cannot form the one defense that has been keeping us safe for thousands of years...our own immune system.

With this note.  Leave no trace camping requires one to eat or bury anything dropped on the ground.  I don't know about you, but backpacking with limited food for weeks on ends means not wasting anything.  I've yet to know anyone who has gotten sick from rinsing, dusting, wiping, or blowing off anything dropped in the dirt from this.  Granted, we don't go around worrying about liquids, or sauces.  Don't fret over spilled milk seems appropriate, but to all else go for it unless your fighting off cancer, have HIV, or are sickly and old i.m.o.

Allen MacNeill
Allen MacNeill

I have six kids and the healthiest one is the one who, when he was a toddler, used to fish moldy grapes out from under the refrigerator and eat them. He apparently followed the "five day rule"

Neil Herbold
Neil Herbold

My lab partners and I performed this same study in my Microbiology class at Morningside College in Sioux city.  We found that the more dry a food was, the less likely it was to pick up bacteria.  We used Chicken Mcnuggets as one of the foods "dropped", and found that if it had not been bitten, it picked up virtually no bacteria.  We used plated E.coli and S.Aureus on HMI agar as our "floors" and then plated them back onto HMI agar to see if they would grow anything.  It's always a fun experiment to do. :)

Fay Watson
Fay Watson

I will be rethinking my 5 second rule...

Keith Robinson
Keith Robinson

I tend to agree with a lot of the feedback --> my grandmother had a saying "you have to eat a peck of dirt before you die" --- thinking that there was a thought to some kind of inoculation process associated with eating food that had been dropped.


The rule typically applied only to food that could be wiped off or washed (are you going to throw away the sirloin steak you just bar-b-qued?). Dropped wet foods would typically be considered gone with the appropriate "don't fuss over spilled milk" statement.


We are surrounded by bacteria --- it is surprising to me that we are not all dead. Perhaps as others have commented, we are too clean for our own good and a bit of common sense should apply to the interpretation of the 5 second rule (which should be a guideline at best --- rules are meant to be broken).

Vivek Sharma
Vivek Sharma

its now a relief that w i m nw able to eat our favourite food dropped on floor which i earlier don't ....

Timothy Barnes
Timothy Barnes

Sorry Sarah. Great job as usual otherwise! Thank you.

Timothy Barnes
Timothy Barnes

The topic was what to do if a cookie is dropped, not a disgusting sandwich with half a container of mustard slathered on it and spilled. The reporter's implication is clear, and the reader's reaction is appropriately disgusted.

Timothy Barnes
Timothy Barnes

The accompanying photo is misleading, and gives a sickening impression. No sane person puts THAT much mustard on a balogna sandwich, let alone recovers, and practically LICKS, it all off the floor with the object of putting such retrieved garbage in one's mouth. The obvious intention of the reporter was to repel the viewer against the notion of picking up such slop on the floor. Had the photo been of a dry piece of toast or a cookie, the readers' reactions might have been different. Personally all of my droppings go straight into the waste receptacle, but to each his own.

Andrew Roberts
Andrew Roberts

Fact is, as a Backpacker- I eat food that has come into contact with dirt etc... all the time.  Don't do it intentionally, but try backpacking in Yosemite and not getting dirt on your food.  


Also- as many articles show we have made ourselves weak to bacteria by using so many antibacterial substances.  If we would not be so paranoid our natural immune systems would kick in.  Don't use antibacterials, do wash hands before eating- and I have not gotten sick in 3 years.


I would never agree to eating wet food that came into contact with the ground though- buttered toast etc...

Dane Udenberg
Dane Udenberg

Seems to me it has a lot more to do with the substance dropped than the amount of time it sits there.  A hard candy can be polished.  A dry cookie can be brushed off pretty effectively.  Items that are softer and moister are just naturally going to pick up more microscopic (and not so microscopic) junk, right from the moment they make contact with a surface.

Donna Cipriano
Donna Cipriano

This Grandma says no to the 5 second rule...sorry!

John Binning
John Binning

At home make another batch. On a canoe trip, rinse and enjoy.

Airotciv Llah
Airotciv Llah

Eating something moist off the floor is disgusting, but if I were hungry enough, I would do it before I starved. 

John Gunnett
John Gunnett

What a lot of people fail to realize is that bacteria is not just on the floor.  How many times do people touch things in public places such as shopping carts, door handles, railings etc...? 


They are all loaded with the same bacteria on the floor and then we wipe our eyes and chew our nails without washing our hands.


How is eating food of the floor any different?

R G
R G

This is all fine and good but, if it drops in the kitty-litter box, it's 3 seconds tops.

suq madiq
suq madiq

How many millions of dollars did they spend to tell you to not eat off the ground like an animal?

Timothy Steele
Timothy Steele

" Hilton, of course, takes the opposite approach: "I have three young boys who have grown up dropping toast on the floor and picking it up again," he says. "In my own home, which I know to be hygienically clean,"

Bullsh*t. Unless of course he lives in a hermetically sealed clean room that has been UV sterilized. Trust me, you have kids in your house, it's got germs.

Frank Shore
Frank Shore

People walk with shoes outdoors on the same ground where animals walk and sometimes lay dead. Cats and dogs can have Salmonella on their feet, and humans can have Salmonella on the bottom of their shoes. Humans walk outdoors where the bodies of dead animals lay. 

If I dropped a food that was moist at all, I would never eat it. If I dropped food that dropped on a floor that was cleaned regularly or was dropped in place that did not have high human traffic, I would pick up the food immediately and examine it for visible transfer. 

If there was visible transfer, I would be leary. I might try to wipe off the visible transfer, and examine the food again.  

I would consider the value of the food, and my own financial situation. I would make a risk-loss calculation. 

I have picked up dry food immediately after dropping it on an unsanitary surface. I have never gotten sick from food I have picked up off the floor, but I realize I am taking a risk. There are times when I will just throw food away that has fallen on the floor. 

If a cut vegetable falls on the floor that I was going to cook. I wash it, dry it with paper toweling, and place it back in the food to be cooked. Any residual bacteria should be killed by the heat. 

There are acids in the stomach that will kill most bacteria. 

I think this is a reasonable approach.

Agurus Guru
Agurus Guru

You pick it up and eat it!  Trouble these days is that people are too clean, therefore have not built up any immunity to everyday bacteria.

James Archbold
James Archbold

As always...no solid answer...gotta love Scientists. " The likelihood of picking up dropped food is directly proportional to how much you paid for it divided by how hungry you are!"  you can quote me on that!

d s
d s

It sounds like these studies didn't investigate the obvious question of if there are bacteria on the floor to begin with. I doubt there is salmonella or e coli on my floor. Why would there be? How long do bacteria survive on the different floor types? The fact that these studies had to put bacteria on the floor to begin with shows that most floors don't have an infestation of bacteria. More worrying than bacteria might be chemicals in the asphalt transferred from the street to your floor by your shoes. But these studies didn't ask the right questions.

t m
t m

Customer to waitress--"What's that fly doing in my soup " ?


Waitress to customer==" Looks like the breast stroke to me "  

Angela lee
Angela lee

@Doris Enders  haha,I'm agree with you the second,not only the bacterial  but the happiness  when we eat is the other side would be considered

Jon Mo'
Jon Mo'

@Keith Robinson It is like what Morgan Freeman narrated at the end of 'War of the Worlds,' "By the toll of a billion deaths, man had earned his immunity, his right to survive among this planet's infinite organisms. And that right is ours against all challenges. For neither do men live nor die in vain."

Janet Jones
Janet Jones

@Frank Shore Examine it for visible transfer?  You must have really good eyes to see the bacteria!  Just sayin' :)

anne boad
anne boad

@Frank Shore  I  don't see a lot of dead animals lying around where people are cooking or eating.

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