5 Second Rule Demystified by a Food Expert

5 Second Rule Demystified by a Food Expert

Does the 5 second rule work?

Does the 5 second rule work?  I think we have all wondered the answer to this question.  How often do you drop food on the floor and debate eating it?

Since I am a Food Scientist, I have been asked this question many times.  My response is always the same, do not eat food that has fallen on the floor.  I have seen many Food Scientists run informal experiments to test out the 5 second rule and it is always debunked. 

I know, I know, it would be easier for all of us if the rule were true, but it is always better to be safe than sorry (or sick 🤪).

What is the 5 second rule?

You probably have dropped food on the floor and still wanted to eat it.  I know I have.

The 5-second rule says the food that has fallen on the floor is safe to eat if it stayed on the floor for five seconds or less  and stayed there for less than 5 seconds is safe to eat. 

Smiling Flask with Orange Liquid

The 5-second rule says the food that has fallen on the floor is safe to eat if it stayed on the floor for five seconds or less  and stayed there for less than 5 seconds is safe to eat. 

Who invented the 5 second rule?

Although the exact origins of the five-second rule are unknown, some believe the idea dates all the way back to Genghis Khan.

Food scientist Paul Dawson and food microbiologist Brian Sheldon trace the origins to stories from that time period as explained in their book.

Does the 5 second rule work?

I wish we could drop things and eat them without any worries. 

Unfortunately, every time someone tests the theory, the 5 second rule is debunked.  Luckily for you, researchers have tested these theories.

 5 second rule Scientific Research

Scientific research has been conducted to test this rule. 

Investigation 1: Germs attach to food

The first study was in 2003.  An intern at the University of Illinois found that gummy bears and fudge-striped cookies picked up E. coli.  The intern placed the gummy bears and cookies on ceramic floor tiles inoculated with the bacteria.  The food was immediately after placing them on the tiles. 

The media picked up this story because it showed that germs attach to foods regardless of the contact time.  

Five second rule image from WikiWorld
5 second rule image from WikiWorld

Investigation 2: Bacteria can live a long time

Next, a 2007 study published in the Journal of Applied Microbiology, showed that bacteria that researchers at Clemson University inoculated tile, wood and carpet floor surfaces with Salmonella. 

In this study, research dropped bologna and bread on the surfaces.  They let the food sit on the contaminated surface for 5, 30 or 60 seconds.  Food picked up 150 to 8,000 bacteria within five minutes. 

This study also found that bacteria could live on dry surfaces for several weeks at levels high enough to quickly transfer to food and cause food poisoning.  

Latest Investigation: What type of food and where it is dropped matters

The latest study was the most comprehensive study on the subject thus far.

In 2016, researchers from Rutgers University dropped four foods onto four contaminated surfaces.  The researchers then varied the time each food was exposed to each of the contaminated surface. 

The first 5 second rule investigation showed that microbes can attach to food
The latest 5 second rule investigation shows the type of food and type of surface impact the transfer of germs.

The time intervals included less than one second, five seconds, 30 seconds and 300 seconds (aka 5 minutes).  This study was the most extensive because each individual scenario duplicated 20 times! 

The study found 3 important things:

  • Contact time did make a difference sometimes. However, some microbial transfer happens instantly
  • The type of food makes a difference on microbial transfer. Higher moisture foods, like watermelon (the wettest food tested) are contaminated at all time intervals and surfaces. 
  • The type of surface impacted the amount of microbial transfer that took place. Carpet had the lowest transfer rates.

How “bad” is it to eat food that falls on the floor? 

Eating any food that falls on the floor is a food safety risk.  Bacteria and germs can attach to food as soon as it hits the floor. 

First, the “5-second rule” has been debunked.  Food that is quickly picked up is likely contaminated.  Studies also indicate that moist or wet foods (example watermelon slice) pick up bacteria even more than dry foods.

the 5 second rule is a food safety risk
The 5 second rule is a food safety risk

Second, the real risk is that the floor may have bacteria that can cause you to get sick.  Visibly dirty floors are an obvious hazard.  However, floors that appear clean can harbor bacteria.  Bacteria that cause food poisoning, such as E. Coli,  can live on surface for months.

Ultimately, the risk is high unless you are sure the floors are free from all bacteria.  The safe choice is to throw out any food you drop on the floor.

Bottom line

Regardless of the risk level, you are still taking a risk every time you decide to eat food that you dropped on the floor. Per food safety basics, you can get sick from food that has fallen on the floor.

If you feel the need to eat dropped food, use common sense.  Your risk level depends on what you drop and where.  Occasionally eating a dry food (like a cracker) that was briefly dropped on a clean floor is likely low risk.  Wetter foods (like fruit) are higher risk.

As the latest study shows, wetter foods are higher risk.  Watermelon (as pictured) had the highest transfer of germs from the floor to the food.
As the latest study shows, wetter foods are higher risk. Watermelon had the highest transfer of germs from the floor to the food.

Remember, bacteria is not visible.  Therefore, it is difficult to judge just how clean a floor is.  A floor that looks clean may still have harmful bacteria present.  Do not make a habit of eating off off the floor.

Lastly, if you are immune-compromised, follow the “zero second” rule. Remember, microbes are not just on floors, kitchen counters can be even more contaminated than the floor.  Follow Food Safety guidelines to keep you and your loved ones safe and healthy.

References

If You Drop It, Should You Eat It? Scientists weigh In on the 5-Second Rule https://aces.illinois.edu/news/if-you-drop-it-should-you-eat-it-scientists-weigh-5-second-rule.  Retrieved 14 September 2020.

Food Safety in the Time of COVID-19: The 5 second rule.  https://fyi.extension.wisc.edu/safefood/2020/04/14/food-safety-in-the-time-of-covid-19-the-5-second-rule/.  Retrieved 14 September 2020.

The Origin Of ‘The Five-Second Rule’ It has to do with Genghis Khan and Julia Child. https://www.sciencefriday.com/articles/the-origin-of-the-five-second-rule/. Retrieved 27 September 2020.

Dawson, Paul and Brian Sheldon.  Did You Just Eat That?: Two Scientists Explore Double-Dippings, the Five-Second Rule, and other Food Myths in the Lab.  USA.  W.W. Norton & Company.  2019.

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