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What Does Science Say About the Five-Second Rule? It’s Complicated

The real world is a lot more nuanced than this simple rule reflects

Aaron Sidder

Many people of all ages agree: Food, when dropped on the floor, remains “good” for five seconds. But this pillar of American folklore, the so-called “five-second rule,” is now under attack from scientists at Rutgers University .

Though the five-second rule may seem like a silly line of inquiry, food safety is a major health burden in the United States. The Centers for Disease Control and Prevention estimate that every year, one in six Americans (roughly 48 million people) get sick from foodborne illness, 128,000 are hospitalized, and 3,000 die.

“We decided to look into this because the [five-second rule] is so widespread. The topic might appear ‘light,’ but we wanted our results backed by solid science,” Donald Schaffner , food scientist at the School of Environmental and Biological Sciences , told Rutgers Today .

Schaffner and his graduate student Robyn Miranda tested different bacteria transfer scenarios using four surfaces (stainless steel, ceramic tile, wood, and carpet) and four foods (watermelon, bread, bread and butter, and gummy candy).

They inoculated each surface with Enterobacter aerogenes —a nonpathogenic “cousin” of Salmonella bacteria that occurs naturally in the human digestive system—and dropped the food on each surface for differing lengths of time (less than one second, five, 30, and 300 seconds). The food samples were then analyzed for contamination. In total, the different combinations of surface, food, and length of contact yielded 128 scenarios, each of which was replicated 20 times. The pair published their results in the journal Applied and Environmental Microbiology .

The duo didn’t necessarily disprove the five-second rule, showing that bacteria transfer does increase with contact time. However, their findings reveal a more nuanced reality than that imparted in common playground wisdom.

“The five-second rule is a significant oversimplification of what actually happens when bacteria transfer from a surface to food,“ Schaffner said. “Bacteria can contaminate instantaneously.”

By food, watermelon collected the most bacteria, and gummy candy the least. According to Schaffner, moisture drives the transfer of bacteria from surface to food; the wetter the food, the higher the risk of transfer.

Looking at the surfaces, tile and stainless steel had the highest rates of contamination transfer. Somewhat surprisingly, carpet had the lowest rate of transfer, and the rate was variable on the wood surface. In the end, they found that many factors contribute to contamination: The length of contact, the characteristics of the surface and the moisture of the food all play a role.

Schaffner and Miranda are the not the first to investigate the five-second rule, but peer-reviewed research is limited. In 2013, the popular MythBusters duo also found that moist foods collected more bacteria than drier foods, and an undergraduate research project tested the rule in an unpublished 2003 study from the University of Illinois. Interestingly, the Illinois study found that women are both more familiar with the rule than men and more likely to eat food off the floor.

Unsurprisingly, the Illinois researchers also found that cookies and candy were more likely to be picked up and eaten than cauliflower and broccoli, which raises an important question. If we really want that food, does it  matter how long it has been on the floor?

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Aaron Sidder | | READ MORE

Aaron Sidder is an ecologist and a freelance science writer based in Denver, CO. He is a former AAAS Mass Media Fellow whose work has appeared National Geographic and Eos.

Does The 5-Second Rule Hold Up Scientifically?

Short answer: it depends on what bacteria are on the floor

By Paul Dawson/The Conversation | Published Sep 15, 2015 7:44 PM EDT

When you drop a piece of food on the floor, is it really okay to eat if you pick up within five seconds? This urban food myth contends that if food spends just a few seconds on the floor, dirt and germs won’t have much of a chance to contaminate it. Research in my lab has focused on how food and food contact surfaces become contaminated, and we’ve done some work on this particular piece of wisdom.

While the “five-second rule” might not seem like the most pressing issue for food scientists to get to the bottom of, it’s still worth investigating food myths like this one because they shape our beliefs about when food is safe to eat.

So is five seconds on the floor the critical threshold that separates an edible morsel from a case of food poisoning? It’s a bit a more complicated than that. It depends on just how much bacteria can make it from floor to food in a few seconds and just how dirty the floor is.

Where did the five-second rule come from?

Wondering if food is still OK to eat after it’s been dropped on the floor (or anywhere else) is a pretty common experience. And it’s probably not a new one either.

A well-known, but inaccurate, story about Julia Child may have contributed to this food myth. Some viewers of her cooking show, “The French Chef,” insist they saw Child drop lamb (or a chicken or a turkey, depending on the version of the tale) on the floor and pick it up, with the advice that if they were alone in the kitchen, their guests would never know.

In fact it was a potato pancake, and it fell on the stovetop, not on the floor. Child put it back in the pan, saying “But you can always pick it up and if you are alone in the kitchen, who is going to see?” But the misremembered story persists .

It’s harder to pin down the origins of the oft-quoted five-second rule, but a 2003 study reported that 70 percent of women and 56 percent of men surveyed were familiar with the five-second rule and that women were more likely than men to eat food that had been dropped on the floor.

So what does science tell us about what a few moments on the floor means for the safety of your food?

Five seconds is all it takes

The earliest research report on the five-second rule is attributed to Jillian Clarke , a high school student participating in a research apprenticeship at the University of Illinois. Clarke and her colleagues inoculated floor tiles with bacteria then placed food on the tiles for varying times.

They reported bacteria were transferred from the tile to gummy bears and cookies within five seconds, but didn’t report the specific amount of bacteria that made it from the tile to the food.

But how much bacteria actually transfer in five seconds?

In 2007, my lab at Clemson University published a study – the only peer-reviewed journal paper on this topic – in the Journal of Applied Microbiology . We wanted to know if the length of time food is in contact with a contaminated surface affected the rate of transfer of bacteria to the food.

To find out, we inoculated squares of tile, carpet or wood with Salmonella. Five minutes after that, we placed either bologna or bread on the surface for five, 30 or 60 seconds, and then measured the amount of bacteria transferred to the food. We repeated this exact protocol after the bacteria had been on the surface for two, four, eight and 24 hours.

We found that the amount of bacteria transferred to either kind of food didn’t depend much on how long the food was in contact with the contaminated surface – whether for a few seconds or for a whole minute. The overall amount of bacteria on the surface mattered more, and this decreased over time after the initial inoculation. It looks like what’s at issue is less how long your food languishes on the floor and much more how infested with bacteria that patch of floor happens to be.

We also found that the kind of surface made a difference as well. Carpets, for instance, seem to be slightly better places to drop your food than wood or tile. When carpet was inoculated with Salmonella, less than 1 percent of the bacteria were transferred. But when the food was in contact with tile or wood, 48%-70 percent of bacteria transferred.

Last year, a study from from Aston University in the UK used nearly identical parameters to our study and found similar results testing contact times of three and 30 seconds on similar surfaces. They also reported that 87 percent of people asked either would eat or have eaten food dropped on the floor.

Should you eat food that’s fallen on the floor?

From a food safety standpoint, if you have millions or more cells on a surface, 0.1 percent is still enough to make you sick. Also, certain types of bacteria are extremely virulent, and it takes only a small amount to make you sick. For example, 10 cells or less of an especially virulent strain of E. coli can cause severe illness and death in people with compromised immune systems. But the chance of these bacteria being on most surfaces is very low.

And it’s not just dropping food on the floor that can lead to bacterial contamination. Bacteria are carried by various “media,” which can include raw food, moist surfaces where bacteria has been left, our hands or skin and from coughing or sneezing.

Hands, foods and utensils can carry individual bacterial cells, colonies of cells or cells living in communities contained within a protective film that provide protection. These microscopic layers of deposits containing bacteria are known as biofilms and they are found on most surfaces and objects.

Biofilm communities can harbor bacteria longer and are very difficult to clean. Bacteria in these communities also have an enhanced resistance to sanitizers and antibiotics compared to bacteria living on their own.

So the next time you consider eating dropped food, the odds are in your favor that you can eat that morsel and not get sick. But in the rare chance that there is a microorganism that can make you sick on the exact spot where the food dropped, you can be fairly sure the bug is on the food you are about to put in your mouth.

Research (and common sense) tell us that the best thing to do is to keep your hands, utensils and other surfaces clean.

This article was originally published on The Conversation . Read the original article .

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The Science Behind the 5-Second Rule

The 5-second rule, a piece of folklore as much a part of our dining lexicon as "bon appétit," offers a curious intersection between science and superstition. This seemingly innocuous belief, that food dropped and quickly retrieved is safe to eat, bridges our understanding of microbiology with our reluctance to waste a perfectly good bite. But how does this rule hold up under the scrutiny of scientific investigation, and what does our adherence to it reveal about human nature? Let's sift through the evidence and societal implications to uncover the truth behind this enduring myth.

Understanding the 5-Second Rule

The 5-second rule is a widely recognized belief suggesting that if food dropped on the floor is picked up within five seconds, it's still safe to eat. Some sources trace the rule back to Genghis Khan, the Mongol ruler who supposedly enacted a much more generous version, allowing food to sit on the floor for hours without worry. Legend has it, this "Khan's rule" was a display of power, showcasing his might and the cleanliness of his floors. Fast forward to modern times, and we're down to a mere five seconds.

Culturally, the 5-second rule reflects our quirky human nature to bend the rules of hygiene for the sake of salvaging that delicious bite, showing just how much we hate to see good food go to waste. It's a testament to our ability to rationalize, or perhaps our hope that not all germs are quick on the draw. Whether at a bustling party or in the quiet corners of the kitchen, invoking the rule prompts nods of understanding, if not always agreement.

Various studies into the rule have given us a mixed bag of results—some say the type of food and flooring can make a significant difference in bacteria transfer, while others suggest time isn't as big a factor as we'd hope. It turns out, some microscopic party-crashers are quite fast on their feet. A study by Rutgers University found that bacteria can transfer to food in less than one second, particularly on tile and stainless steel surfaces. 1

Still, despite evidence suggesting we might be better off not eating that floor-bound french fry, the rule persists. It stands as a cultural phenomenon, reflecting society's collective bargain with the microscopic world: "If we're quick enough, maybe we'll get away with it this time."

Scientific Investigations into the 5-Second Rule

Scientists have tackled the 5-second rule by setting up various real-world scenarios to scrutinize the belief's scientific standing. By meticulously dropping different types of food on assorted surface materials, from stainless steel to carpet, these trials bring light to our understanding of bacterial transfer rates. Key in these studies is the attention to detail in the selection of foods, ranging from moisture-rich watermelon to drier, harder substances like cookies, offering a broad spectrum for analysis.

One noteworthy methodology involved clocking the exact duration food items remained in contact with floors, varying timings from below one second to over 30 seconds, to see if and how the duration influenced bacterial hitchhiking from floor to snack. This method tapped into the crux of the 5-second premise by benchmarking the safety window—if any exists—for consuming dropped food.

Bacteria playing pivotal roles in these scrutinies included notorious culprits like Escherichia coli and Staphylococcus aureus, whose presence on food can spell trouble. By culturing samples after food-floor contact, researchers could concretely measure how much of these unwanted guests transferred within different time frames. Such rigorous contamination checks offer tangible proof either damning or supporting the infamous rule.

Surfaces under the microscope weren't spared scrutiny either. The experiments considered diverse environments where dropping food might occur, comparing how bacterial communities differ between, say, wooden panels and tiled flooring or how a carpet's fuzzy architecture might surprisingly act as a bacterial barrier, contra to hard, slick surfaces that seemingly invite more microbial passengers.

This deep dive into various setups mimics real-life fumbles, providing a rich database on how our home's architectural choices can stealthily influence our health when snacks go astray. As findings from these explorations weave into the public perception, they enrich our discourse on hygiene practices. Whether or not the studies collectively trash or treasure the 5-second rule, they undeniably feed our curiosity and drive an appetite for informed choices in our daily lives.

Factors Influencing Bacterial Transfer

Flooring types play a massive role in how much bacteria hops onto your snack. Picture this: a juicy grape rolls off the table. If it lands on a plush carpet, less bacteria will likely make it a new home compared to if it smacks onto the kitchen tiles. Carpets, with their fibers, might seem like bacteria's best hideout, but they don't pass on as many germs to the food. That's because the carpet fibers decrease the actual surface area touching the food. On the flip side, hard surfaces like tiles give bacteria the red carpet treatment straight onto whatever dropped.

Now, let's talk about wet versus dry foods. If you drop something dry, like a cracker, the bacteria are less likely to hitch a ride on it. Think of the cracker as a desert – not much sticks in a dry environment. But let's say you drop a slice of watermelon. That's practically a pool party for bacteria. The moisture steers bacteria onto and into the food much quicker, making wet or moist foods more likely to grab a bunch of unwanted microscopic guests.

The seconds are ticking, but how many seconds until it's too late? You've heard the rule: "5 seconds, safe to eat; more than that, defeat." However, the grim reality is bacteria transfer can happen in less than those famous five seconds, especially on those non-carpeted, unforgiving surfaces. The length of time food dances with the floor does more than just decide its fate—it ramps up the bacterial count the longer it stays down there. A study published in the Journal of Applied Microbiology found that Salmonella Typhimurium can survive for up to four weeks on dry surfaces and can be transferred to food immediately upon contact. 2

Given these tidbits of knowledge, the next time your favorite snack decides to take a tumble, you might weigh your next move a bit more carefully. Whether it's the heartbreak of saying goodbye to that last piece of pizza or the quick snatch and eat, remembering these key factors about moisture content, surface type, and contact time could make all the difference in the microscopic jungle we call home. So next time something drops, think fast, assess the scene, and maybe, just maybe, let that 5-second rule slide in favor of safety.

Health Risks Associated with the 5-Second Rule

When food gets cozy with the floor, it's like inviting microbes to a party. Think about the last time you dropped a slice of apple. Chances are, microscopic gate-crashers didn't wait for five seconds to hitch a ride. These unwanted guests can include more than just E. coli and Staphylococcus aureus, which were mentioned earlier. Here's a list of other potential party-crashers:

• Salmonella: Found mostly in raw poultry and eggs, it can make camp on countertops and floors, waiting for a free ride. Got an upset stomach, fever, or worse after eating that floor-touching pretzel? Salmonella could be the culprit.
• Listeria: Notorious for living it up in cooler temps, it's that uninvited guest that doesn't need much to thrive and is particularly fond of deli meats and soft cheeses.
• Norovirus: Often dubbed the stomach flu, this highly contagious virus needs but a brief encounter to spread. A chip falling on an area previously touched by an infected person can become a vehicle for this virus.
• Campylobacter: Mostly lurking around raw and undercooked poultry, it's got a talent for causing diarrhea, fever, and abdominal cramps.
• Hepatitis A: Spread through microscopic bits of poop, it loves the low-key lifestyle on surfaces waiting for a lift. Reach for that floor-touched apple slice and you might just get more than you bargained for.
• Giardia: This parasite prefers the water to party in but won't say no to a quick mingle on your kitchen floor, especially around pet food bowls.

Bottom line: When your food hits the deck, think beyond the 5-second rule. These tiny intruders don't play by the rules and can gate-crash within milliseconds. Whether it's a tile or carpet, a piece of hard candy or a slice of bread hitting the floor spells bad news in terms of hygiene. It's always better to err on the side of caution than to invite these unseeable party-ruiners into your system. So next time, maybe let that piece of food go and spare yourself a possible trip down sick lane.

Public Perception vs. Scientific Reality

Despite the wealth of evidence challenging the validity of the 5-second rule, many continue to follow it based on tradition or convenience. This disconnect between scientific findings and public behavior reveals underlying factors that propel people to stick with the rule. One such factor is the overestimation of personal hygiene – individuals may assume their homes are cleaner than average, reducing perceived risks. Psychological comfort plays a role too; the minor rebellion of breaking a 'food safety' rule without immediate consequences can provide a sense of thrill. Social pressures also influence decisions. In a group setting, someone might apply the 5-second rule to avoid wasting food or to seem laid-back.

Risk assessment varies; people may consider the nutritional value of the dropped item and its scarcity before deciding. The allure of a delicious piece of food might outweigh hygiene concerns for some, underlining the clash between desire and rational health precautions. Humans show a remarkable willingness to engage in 'magical thinking,' where arbitrary rules are believed to provide control over uncontrollable situations. This cognitive bias assures some that a quick response can magically prevent contamination.

Disparities in education about food safety can lead people to underestimate risks. Misinformation or lack of awareness about how quickly bacteria can transfer to food often leads to misplaced confidence in the 5-second rule's effectiveness. People's faith in their immune systems also sways decisions; those who believe in their body's ability to fight off germs might see little harm in eating dropped food. These psychological and social constructs explain why the 5-second rule persists despite scientific debunking.

Curiosity about the truth of this rule doesn't necessarily lead to behavior change, evidencing the complex relationship between knowledge and action. Education on the subject often meets cognitive dissonance, where conflicting beliefs create discomfort, leading individuals to disregard new information that contradicts their prior habits. This psychological phenomenon solidifies adherence to the rule, as it's easier to dismiss scientific evidence than reevaluate personal beliefs and behaviors. A survey conducted by the Food and Brand Lab at Cornell University found that women were more likely to eat food dropped on the floor, with 55% of women versus 38% of men invoking the 5-second rule. 3

Addressing this gap requires more than sharing facts; it calls for nuanced understandings of human behavior, aimed at reshaping norms around food safety from the ground up—literally. Providing practical, relatable alternatives to the rule, like quickly rinsing the dropped item, if appropriate, could bridge this divide, aligning public behavior with scientific advice for healthier eating practices.

In the grand scheme of things, the 5-second rule serves as more than just a decision-making tool for eating dropped food; it's a mirror reflecting our complex relationship with hygiene, risk, and waste. Despite the clear warnings from science, our collective willingness to gamble with microscopic dangers underscores a fascinating aspect of human behavior. Perhaps the most crucial takeaway is not whether we should eat food off the floor, but rather understanding why we're tempted to in the first place. This insight into our psyche may just be the key to fostering healthier, more informed decisions about what we choose to put in our mouths.

• Miranda, R. & Schaffner, D. (2016). Longer Contact Times Increase Cross-Contamination of Enterobacter aerogenes from Surfaces to Food. Applied and Environmental Microbiology, 82 (21), 6490-6496.
• Dawson, P., Han, I., Cox, M., Black, C., & Simmons, L. (2007). Residence time and food contact time effects on transfer of Salmonella Typhimurium from tile, wood and carpet: testing the five-second rule. Journal of Applied Microbiology, 102(4), 945-953.
• Spizman, R. E. (2003). Survey: women more likely than men to eat food fallen on floor. Shape Magazine.

January 18, 2017

Is the 5-Second Rule True?

Should you really abide by the famous 5-second rule?

By Everyday Einstein Sabrina Stierwalt

Most of us have heard it: if you drop food on the floor, it’s still okay to eat it, as long as you act quickly and pick it up within five seconds of it hitting the ground. But does the so-called “five-second rule” have any scientific backing? Anecdotally, most of us would agree—it depends on the kind of food. I’m more likely to eat a cracker that I’ve dropped on the floor than I am, say, a buttered bagel that lands spread-side down. But does timing also make a difference? Is there really a delay or grace period before which germs can find their way to your fallen food?

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Science News Explores

The five-second rule: microbes can’t count.

Other scientists have studied the five-second rule and agree — it’s a lie

I swabbed bologna for science. Other scientists have tried testing the five-second rule with bread, watermelon and gummy candies.

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By Bethany Brookshire

September 13, 2017 at 9:15 am

This article is one of a series of Experiments meant to teach students about how science is done, from generating a hypothesis to designing an experiment to analyzing the results with statistics. You can repeat the steps here and compare your results — or use this as inspiration to design your own experiment. 

View the video

Everyone has dropped food on the floor. And many might think that if they pick it up quickly, microbes haven’t had time to crawl on. The latest DIY Science video tests this “five-second rule” with an experiment. Previous blog posts in this series detail how that experiment was designed and conducted . The experiment’s results showed that five seconds on the floor or not, all of the food hosted germs.

Others have tested the five-second rule, too! The general conclusion from them all is that microbes aren’t waiting to count to five. Once food has hit the floor, maybe it’s best to let it lie.

Jillian Clarke tested the five-second rule in 2003. The then-high school student was doing summer research in the lab of Hans-Peter Blaschek. He is a food scientist at the University of Illinois, Urbana-Champaign. Clarke covered smooth and rough flooring tiles with bacteria. Then she dropped gummy bears and fudge cookies on the tiles. The teen found that after five seconds, the cookies and candy had picked up bacteria. Also, more bacteria was transferred onto gummy bears when they fell onto smooth tiles than rough ones.

Adult scientists have also taken on the rule. Paul Dawson and a group of food scientists at Clemson University in South Carolina smeared Salmonella — a type of bacteria that can cause disease — onto carpet, wood and tile. The researchers then dropped bologna and bread.

The longer the bacteria had been left to dry on the floor, the fewer microbes that ended up on the food. The carpet transferred fewer germs to the bologna than did the other surfaces, the team found. And food that had been left on the surfaces longer picked up more bacteria. But picking up food before five seconds had passed didn’t keep them clean. Bologna and bread both picked up germs during that time. Dawson and his food-dropping fellows published their results October 6, 2006 in the Journal of Applied Microbiology .

Robyn Miranda and Donald Schaffner dropped food onto floors for science at Rutgers University in New Brunswick, N.J. The scientists tested strawberry gummy candy as well as watermelon, bread and buttered bread. They dropped the foods onto different surfaces contaminated with bacteria — steel, tile, wood and carpet. They let the food lie there for times ranging from five seconds to as long as five minutes.

All picked up microbes, but the winner was watermelon. That fruit became covered in bacteria no matter the surface. The researchers also showed that carpet transferred the fewest bacteria. And while longer times meant more germs, anything longer than a second was long enough for microbes to hop on board. The scientists published their results September 2, 2016 in Applied and Environmental Microbiology. 

The most famous test of the five-second rule , though, comes from the television show Mythbusters . Hosts Jamie Hyneman and Adam Savage contaminated floor tiles with bacteria. Then they dropped crackers and pastrami, picking up the food after two or six seconds. The Mythbusters also had a control in which the food wasn’t dropped at all. They found that all of their samples picked up bacteria, just as in our experiment. Wet pastrami picked up the most. And so Hyneman and Savage declared the myth busted.

Limitations and lessons learned

Our experiment’s results are similar to those of other scientists. We all showed that food has bacteria riding along, whether it’s been dropped for a while, picked up immediately, or never dropped at all.

Of course, no study is perfect. Ours certainly wasn’t. Here are just a few of the problems, or limitations:

• I only dropped my bologna on tile. People drop food on all sorts of surfaces, from carpet to dirt.
• I only tested bologna, instead of several wet and dry foods.
• Like the Mythbusters, I counted bacterial colonies. However, I don’t know which species I was able to grow. And I couldn’t separate bacteria from fungus, which also grew on the plates.
• I tried to create a very clean environment, but the controls show that I didn’t quite succeed.
• I tested clean and dirty floors, but I didn’t know exactly how clean or dirty that floor was. Other scientists solved this by contaminating their floors in a more controlled way.
• I knew exactly what I was testing and what to expect. In other words, I was not blind to the conditions. Because I knew what I was looking for, I could have brought bias into my results.

If I were to do this experiment again, I could try to fix these problems. I could add more flooring types and more food types. I could spread bacteria on my floor beforehand, rather than the contents of my compost pile.

But with other studies showing similar results, all the data declare: This myth is BUSTED! Food has bacteria on it, dropped or not. The bugs will most likely never cause you problems. But microbes certainly aren’t waiting five seconds before colonizing a new bologna world.

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‘Five-Second Rule’ for Food on Floor Is Untrue, Study Finds

By Christopher Mele

• Sept. 19, 2016

You may think your floors are so clean you can eat off them, but a new study debunking the so-called five-second rule would suggest otherwise.

Professor Donald W. Schaffner , a food microbiologist at Rutgers University in New Jersey, said a two-year study he led concluded that no matter how fast you pick up food that falls on the floor, you will pick up bacteria with it.

The findings in the report — “Is the Five-Second Rule Real?” — appeared online this month in the American Society for Microbiology’s journal, Applied and Environmental Microbiology .

Researchers at Aston University’s School of Life and Health Sciences in England reported in 2014 that food picked up a few seconds after being dropped is “less likely to contain bacteria than if it is left for longer periods of time,” giving rise to news accounts suggesting that eating the food might be harmless. Those findings, and research done at the University of Illinois in 2003, did not appear in a peer-reviewed journal, Professor Schaffner noted.

Even though the five-second rule is a bit of folklore, it still raised important public health issues that demanded closer scrutiny, he said. He cited research by the Centers for Disease Control , which found that surface cross-contamination was the sixth most common contributing factor out of 32 in outbreaks of food-borne illnesses.

How was the study conducted?

Professor Schaffner and a master’s thesis student, Robyn C. Miranda, tested four surfaces — stainless steel, ceramic tile, wood and carpet — and four different foods: cut watermelon, bread, buttered bread and strawberry gummy candy . They were dropped from a height of five inches onto surfaces treated with a bacterium with characteristics similar to salmonella.

The researchers tested four contact times — less than one second and five, 30 and 300 seconds. A total of 128 possible combinations of bacterial preparation, surface, food and seconds were replicated 20 times each, yielding 2,560 measurements.

What did the study find?

The research found that the five-second rule has some validity in that longer contact times resulted in transfer of more bacteria. But no fallen food escaped contamination completely. “Bacteria can contaminate instantaneously,” Professor Schaffner said in a news release.

Carpet had a very low rate of transmission of bacteria compared with tile and stainless steel; transfer rates from wood varied.

The composition of the food and the surface on which it falls matter as much if not more than the length of time it remains on the floor, the study found. Watermelon, with its moisture, drew the highest rate of contamination and the gummy candy the least.

In an interview, Professor Schaffner said, “I will tell you on the record that I’ve eaten food off the floor.” He quickly added: “If I were to drop a piece of watermelon on my relatively clean kitchen floor, I’m telling you, man, it’s going in the compost.”

Where did the rule get its start?

The history of the five-second rule is difficult to trace but it is attributed apocryphally to Genghis Khan, who declared that food could be on the ground for five hours and still be safe to eat, Professor Schaffner said.

Why do people do this anyway?

William K. Hallman , an experimental psychologist and a professor at the Department of Human Ecology at Rutgers University, said people do not put every decision through a risk-benefit filter and instead rely on cognitive shortcuts called heuristics to help in their daily lives.

“It’s a way of making a very quick decision with whatever data is available,” he said in an interview.

But sometimes those shortcuts can be based on flawed assumptions or missing information.

For instance, germs are invisible and so they are easy to ignore when “something of particular value, like a yellow peanut M&M” falls to the floor, he said. Because germs are out of sight, the belief is there is no harm in picking up the M&M and popping it in your mouth.

Douglas Powell , a former professor of food safety and the publisher of barfblog.com about food safety, added that people eat from the floor because they are told not to waste food.

People are also impervious to risk. “I’ve done this all my life and never gotten sick; I did this a couple of days ago and nothing happened,” he said in an email.

Or as Professor Schaffner observed: “The first kid, the pacifier falls on the floor, oh my God, we have to sterilize it. By the third kid, it’s like ‘whatever.’ ”

Shouldn’t people know better than to eat off the floor?

Research has shown that people think germs belong to other people, Professor Hallman said. For instance, people generally believe their bathrooms are cleaner than a public restroom. In fact, that is not the case because public restrooms are cleaned more regularly, he said in an interview.

People also misunderstand the transmission of germs.

“We sort of joke about the five-second rule, but people act as if germs take some period of time to race to the item that fell on the floor,” he said.

People also do not recognize the symptoms of food-borne illnesses and tend to blame them on the last thing they ate, so they do not connect how their earlier actions might have made them sick.

Are men more likely to eat off the floor than women?

Yes, according to Professor Hallman. In contrast to women, men say they more frequently engage in behaviors such as picking up food or a fork that has fallen to the floor, or picking an insect or a hair out of their food then continuing to eat, he said. The findings came from a phone survey of 1,000 Americans in 2005.

Anthony Hilton , a professor of microbiology at Aston University, said a survey of nearly 500 people found 81 percent of women said they followed the rule — they would not eat anything that lingered on the floor — compared with 64 percent of men, the magazine “Scientific American” reported.

“Hilton says he doesn’t have a good explanation for this gender differentiation but points out that this finding is consistent with other research into the five-second rule,” the magazine wrote. “One possible conclusion: This is tacit confirmation of another piece of folk wisdom — men are less discerning when it comes to their food’s cleanliness.”

An earlier version of this article omitted one of the factors that researchers at Rutgers University assessed in their report “Is the Five-Second Rule Real?” about what happens to food dropped on a floor. Two types of bacterial preparation were evaluated in addition to how long food remained on the floor, the types of food and the kinds of surfaces where it landed.

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E. Coli: The bacteria, which has recently been found in ground beef and walnuts, sickens an estimated 265,000 Americans each year .

Norovirus: The virus is extremely contagious, and, as anyone who has had it can tell you, extremely unpleasant .

Salmonella: People often get sick with salmonellosis, the infection caused by the bacteria, after eating undercooked meat or other contaminated foods .

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Science News for Students

Designing your own experiment to debunk the ‘five-second rule’

We’ve all been there. You’re excited to take a bite out of your lunch, but then it drops on the floor. You quickly pick it up, but — is it safe to eat?

In Eureka!Lab’s second DIY Science video, science education writer and resident scientist Bethany Brookshire puts the  five-second rule  to the test. Bethany finds that bacteria don’t really wait for the count of five. If food has fallen, it probably has microbes all over it.

The video and accompanying blog posts walk you through how to design an experiment, grow your own microbes, and analyze results to test whether food left on the floor for only five seconds picks up fewer microbes than food left longer.

View the video below:

Read the blog posts:

• The five-second rule: Designing an experiment
• The five-second rule: Growing germs for science
• The five-second rule: Myth busted?
• The five second rule: Microbes can’t count

Happy experimenting! And hang onto your food.

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The Origin Of ‘The Five-Second Rule’

It has to do with Genghis Khan and Julia Child.

First Known Use:

The first written reference to a “rule” about the acceptability of eating dropped food appeared in 1995 —but the household guideline was already long in the making.

Whether you call it the five-second rule, three-second rule, or the ____-second rule, you know what this rule is. Someone drops a tasty morsel of food on the ground and scoops it right back up, declaring that, according to the “rule,” there was no time for the bacteria to glom onto the treat. As usual, the history of this idiom is a little more complicated than that, and the science is, too. Is there any scientific validity to the five-second rule?

Genghis Khan, Julia Child, And The Five-Second Rule

The five-second rule as we know it today has murky origins. The book Did You Just Eat That? by food scientist Paul Dawson and food microbiologist Brian Sheldon traces the origins to legends around Genghis Khan. The Mongol ruler is rumored to have implemented the “Khan Rule” at his banquets. “If food fell on the floor, it could stay there as long as Khan allowed,” write Dawson and Sheldon. The idea was that “food prepared for Khan was so special that it would be good for anyone to eat no matter what.”

“In reality,” they write, “people had little basic knowledge of microorganisms and their relationship to human illness until much later in our history. Thus, eating dropped food was probably not taboo before we came to this understanding. People could not see the bacteria, so they thought wiping off any visible dirt made everything fine.”

Roughly six centuries after Khan’s death, germ theory evolved into, as the Encyclopedia Britannica writes, “perhaps the overarching medical advance of the 19th century.” Researchers determined that tiny, invisible microorganisms caused certain diseases and infections—and French chemist Louis Pasteur proved that those same kinds of microorganisms are behind both wine fermentation and the souring of milk. But despite knowing that germs are everywhere, it can still be tough to walk away from a tempting treat that slipped through one’s fingers.

We see the rule pop up once again in a 1963 episode of Julia Child’s cooking show The French Chef , which may have helped canonize the attitude, if not the phrase, into popular imagination. The famous chef attempted to flip a potato pancake in a pan, but she missed, and the pancake landed squarely on the stovetop.

“When I flipped it, I didn’t have the courage to do it the way I should’ve,” Child said. “But you can always pick it up if you’re alone in the kitchen. Who is going to see?”

The flopped pancake sits on the stovetop for about four seconds before Child tosses it back into the pan, but by the time the phrase begins to solidify and appear in print, people take their own liberties with the exact amount of acceptable seconds. According to the Oxford English Dictionary , the first mention in print of some sort of rule came from the 1995 novel Wanted: Rowing Coach , which referenced a “twenty-second rule.” A few years later, in the 2001 animated film Osmosis Jones , a character follows the “ten-second rule” and eats a germ-infested egg, which sends his body’s immune system into disarray.

So, Is The Five-Second Rule Actually Real?

Robyn Miranda, a Ph.D candidate in food science at Rutgers University, published a study in Applied and Environmental Microbiology with her adviser that scientifically investigated the validity of the five-second rule.

“It was not what I expected to do for my master’s,” she says. “We saw this as a really important opportunity to look at this rule that people truly follow, that consumers really use. So, let’s see if this matters, from a public health standpoint.”

Miranda stocked up on four different food types: watermelon, bread, bread and butter, and gummy candy. Then, she methodically dropped each food onto one of four surfaces typically found in kitchens—stainless steel, tile, wood, and carpet—and let each food item sit for exactly less than a second, five seconds, 30 seconds, and five minutes to measure bacterial transmission. Miranda and a team of undergraduates did 20 replicates of each food, on each surface, for each length of time, over the course of six months. “I’m not going to lie; doing the experiments lost its luster after a while,” she says. “But the results were very interesting.”

The Science Behind The Five-Second Rule

Wearing a food seat belt.

While microorganisms are to blame for infections, not all bacteria are created equal.

“We carry four pounds of bacteria around with us on our bodies all the time,” Paul Dawson tells Science Friday.  “And we have more bacterial cells in and on our body than we have our human cells—so we’re kind of in symbiotic relationship with it. And we’re more and more finding they are part of our health, the delicate balance there, so to speak.”

There is some truth to the idea that exposure to certain bacteria and compounds can help build immunity, says Dawson. But we also know that people can become seriously sick from certain infections, so random exposure may not be the best practice. Dawson compares eating food off the floor to wearing a seatbelt: “You probably could do both of those your whole life and never be injured or get sick, but we know with the seat belt that if you have an accident or there is bacteria there, you’re going to be exposed to it.”

“Speaking specifically about the five-second rule and when eating food off the floor, probably in reality there’s not much risk in that,” he says. “But I don’t know if there’s much to be gained either though, as far as immunity.”

But often, it’s not immunity that’s in the forefront of people’s minds when a morsel hits the floor.

“I don’t eat food off the floor, but I also don’t drop food on the floor,” says Robyn Miranda. “But if I [did], it would depend.” Watermelon? No way, she says. Skittles? Maybe. “I guess you’d be surprised what people will do for a food that they care about.”

Sources And Further Reading

• Special thanks to Robyn Miranda and Paul Dawson
• Did You Just Eat That? Two Scientists Explore Double-Dipping, the Five-Second Rule, and Other Food Myths in the Lab by Paul Dawson and Brian Sheldon
• “Longer Contact Times Increase Cross-Contamination of Enterobacter aerogenes from Surfaces to Food” (American Society for Microbiology: Applied and Environmental Microbiology)
• “History of medicine: Verification of the germ theory” (Encyclopedia Britannica)
• The Oxford English Dictionary

Meet the Writer

About johanna mayer.

Johanna Mayer is a podcast producer and hosted Science Diction from Science Friday. When she’s not working, she’s probably baking a fruit pie. Cherry’s her specialty, but she whips up a mean rhubarb streusel as well.

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Does double-dipping a chip really infect the dip? Is the five-second rule real? Plus, a look at other food myths.

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Ghenghis Khan Is Responsible For The 5-Second Rule

E veryone's a little clumsy sometimes, and if you've ever dropped food on the floor, you've probably thought of the five-second rule. It's a nigh-universal concept — a law that is ingrained in us from our playground days, watching classmates fumble their lunch. Many of us have continued to ascribe to the five-second rule into our adulthoods, and at this point, it's become a piece of folk wisdom. But it really shouldn't be. Multiple studies have debunked the five-second rule, so how did we become so convinced of it?

Food scientists Paul Dawson and Brian Sheldon explored the origin of the five-second rule in their book "Did You Just Eat That?,"  tracing the aphorism to, of all people, Ghengis Khan. It is said that the Mongol ruler imposed a rule at banquets that any piece of food dropped on the floor could remain there as long as the Khan allowed and still be edible. Food for the Khan was of such quality that it would always be good, it was thought. However, some versions of the story suggest that people who followed the rule and subsequently died of food poisoning were said to have been "Khanned".

This is a far more lenient law than the five-second rule, but Khan ruled in the early 13th century, and germ theory would not be discovered for another 600 or so years. Of course, that would not stop us from nibbling scraps off the floor, and believe it or not, the term "five-second rule" came about over a century after we learned about germs.

Read more: Myths About Garlic You Thought Were True

The History Of The Five-Second Rule

The five-second rule wouldn't be the first time Ghengis Khan influenced our eating habits — he also played a role in the history of burgers  — but it's unclear if this adage really stems from him. The story is a bit muddled, with some versions saying that the Khan had a 12-hour rule and others saying it was indefinite.

Throughout history, variations of the five-second rule continued to pop up. It's said that when Michelangelo was painting the Sistine Chapel ceiling, there was a 25-minute rule because if food were dropped from the top of the scaffolding, it would take 25 minutes to climb all the way down and retrieve it. A couple of centuries later, during the American Revolution, a one-minute rule was imposed, mainly because any food left on the floor for longer than that would be swooped up by dogs.

The famed chef Julia Child would prove instrumental in developing the five-second rule. In an episode of her show, "The French Chef," Child fumbled a pancake flip, dropping some on the stovetop (but not on the floor, as inaccurate retellings of the story have claimed). She calmly flipped it back into the pan, assuring her audience that, "You can always pick it up, and if you're alone in the kitchen, who is going to see?" Unfortunately, when it comes to eating dropped food, being seen is the least of your worries.

Don't Trust The Five-Second Rule

Unfortunately, the five-second rule doesn't hold up to science. It was put to the test in 2003 by Jillian Clarke, a high school student working as a research apprentice at the University of Illinois. In an interview with NPR , Clarke explained that she dropped gummy bears and cookies onto floor tiles, checking them for bacteria after varying time intervals. She found that the foods became contaminated with microorganisms regardless of how long they spent on the floor.

Subsequent research has backed up Clarke's findings. A 2016 study published in Applied and Environmental Microbiology revealed that foods can be contaminated the moment they hit the floor, although the longer you leave it there, the more bacteria will accumulate. While studies caution against trusting the five-second rule, it is dependent on a few factors. The most important is the cleanliness of the floor the food was dropped on, so it's essential to keep a clean kitchen (not just the floors, but all the surfaces food might touch). Certain floor surfaces also appear more risky, with tile and wood typically causing more contamination than carpet. Several studies found that the drier the food, the less bacteria it picks up, because bacteria are transferred through water. Drop a cracker, and the five-second rule might be okay, but drop a piece of meat, and you'd best just throw it out.

Read the original article on Chowhound

Think Twice

The five second rule.

Source: It’s Interesting

Nicole Kell

Most have us grown up hearing about the “five-second rule”. Simply put, people say that food is safe to consume if it is snatched up from the ground in five seconds or less.

But is the food really safe to eat or should we throw it away?

High school student Jillian Clarke and Dr. Meredith Agle at the University of Illinois at Urbana-Champaign performed an experiment to determine whether it is safe to eat food that has been on the ground. Jillian swabbed the floors of a lab, hall, dormitory, and cafeteria in order to quantify the number of organisms. She repeated this and then examined swabs from both trials. The swabs showed minimal microorganisms. The lack of microorganisms on the floor is due to the fact that floors she was testing were dry and most pathogens such as E.coli and salmonella only survive in moist conditions.

However, it has been proven that when it comes to damp floors and carpet, or moist and sticky foods such as gum, watermelon and ice cream, all bets are off when it comes to the “five second rule”. A professor from Clemson University performed a similar experiment, but on different types of surfaces. He found that it didn’t matter how long the food was on the floor, but the amount of bacteria on the floor and the moisture of the food/floor play a significant role how much bacteria transferred to the food.

When it comes to the spread of bacteria and eating food off of the ground, researchers and doctors advise people to throw away the food in order to avoid risk of illness.

https://www.webmd.com/a-to-z-guides/features/5-second-rule-rules-sometimes-#1

https://www.ahchealthenews.com/2017/09/12/five-second-rule-myth/

https://mysteriousuniverse.org/2016/09/the-five-second-rule-is-a-myth/

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Researchers Reveal the Truth About the ‘Five Second Rule’

• September 26, 2016

Unfortunately, researchers have now proven that the ‘five second rule’ for eating food off the floor is, in fact, not scientifically accurate.

The time it takes bacteria to transfer onto food can actually be less than one second, according to researchers at Rutgers University led by professor Donald Schaffner, an extension specialist in food science.

A ‘Pop Culture’ Myth

“The popular notion of the ‘five-second rule’ is that food dropped on the floor, but picked up quickly, is safe to eat because bacteria need time to transfer,” said Professor Schaffner.

“We decided to look into this because the practice is so widespread. The topic might appear ‘light’ but we wanted our results backed by solid science,” he added.

Their first findings confirmed that moisture, surface type and the fabled contact time all have a part to play in cross contamination.

Those variables were explored further by testing four food types (watermelon, bread, bread and butter, and gummy sweets), four surfaces (ceramic tiles, wood, stainless steel and carpet) and four contact times (less than one second, 5 seconds, 30 seconds, 300 seconds) at the university labs in New Brunswick.

So what did they find?

Watermelon was the most easily contaminated food, which led researchers to conclude that moisture is the strongest player in terms of cross contamination. If you do drop your watermelon, though, make sure it’s on a carpet, which had lower transfer rates than stainless steel and ceramic tiles. Gummy sweets were found to be the safest food to drop.

“Bacteria don’t have legs, they move with the moisture, and the wetter the food, the higher the risk of transfer,” Professor Schaffner said. “Also, longer food contact times usually result in the transfer of more bacteria from each surface to food.”

He went on to say that, in essence, the five second rule is an oversimplification of what actually happens when bacteria transfer from a surface to food.

So in a way we were right all along. Kind of.

Author: Ryan Child

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