The Five-Second Rule Redux

Wherever you are reading this, look down and ask yourself if, under any circumstances you would be willing to get down on your knees and lick the floor. If the answer could ever be yes or even maybe, then you can stop reading right here - you might consider getting some professional help.

Almost everyone is familiar with the “Five Second Rule” which states that food that has fallen on the floor is safe to eat if it is picked up in 5 seconds or less. Most of us outgrow the urge to eat food off the floor or invoke the five second rule sometime before the second decade of life and yet the controversy remains. It is one of those odd little human behaviors that crosses age and cultural lines and touches on important issues relating to hygiene, health, risk taking behavior, and taste.

In 2005, Jillian Clarke was awarded the Ignoble Prize for her study of the scientific basis of the Five Second Rule which she undertook as a summer intern at the University of Illinois at Urbana-Champaign. She measured the bacterial contamination on the floors, the transfer of bacteria to cookies and gully bears, and the beliefs of students around the five second rule. Here is what she found:

• Seventy percent of women and 56 percent of men are familiar with the 5-second rule and use it to make decisions about eating food off the floor.
• University floors are remarkably clean from a microbial standpoint.
• Women are more likely than men to eat food that’s been on the floor.
• Cookies and candy are much more likely to be picked up and eaten than cauliflower or broccoli.
• Food dropped on the floor is contaminated in 5 seconds or less.

If the floors at the University of Illinois are typical, your chances of getting a bacterial gastroenteritis like salmonella, campylobacter, or e. coli from eating food off the floor is relatively slim. This may not be the case everywhere and it doesn’t address the question of viral illness such as Norovirus. Also, you if you feel the need to eat food that has fallen on the floor you don’t need to dive after it - by five seconds bacterial contamination has already occurred.

These findings are supported by a second, a more comprehensive study reported in the Journal of Applied Microbiology last year in which pieces of bread and bologna were dropped on carpet, tile, and wood floors that had been contaminated with salmonella. They also found that by 5 seconds the food was just as contaminated as it was at 60 seconds, so again, if it is your bent to eat dropped cold cuts, you may as well take your time. They did find that the longer that they waited to drop the food after contaminating the floor with bacteria, the less that ended up on the food, so if you have any choice in the matter, wait as long as possible before dropping your food. It wasn’t much of a reduction but it might make the difference between getting sick and getting with it again.

If you do get sick from eating off the floor, it is very likely that you will get what is known as an acute Gastroenteritis or “stomach flu“. Most of these go unreported but estimates are that there are about 100 million cases in the US every year and that most of these are viral due to either Norovirus or rotavirus. There are several million cases that are bacterial and somewhere around 10,000 deaths are reported every year. All things being equal, (which they are not) this means that your chance of catching the stomach flu is about 1 in 4 every year and the risk of death from bacterial gastroenteritis is about 1 in 40,000. You take a much greater risk of death getting in your car and driving to dinner than you would if you chose to eat your dinner off the floor. Not very much of a risk as risk taking behavior goes.

That’s the state of the art in terms of the science of the five second rule. In the end it is a matter of personal choice. You may or may not get sick; that depends on what else has dropped on that particular patch of floor, how long it has been since it was dropped, and a lot of other things that we can group together and call luck. Even if you do get sick you probably won’t die as the result of invoking the five second rule. The good news is that the next time some tasty morsel or gummy worm escapes and hits the floor, you needn’t leap for it. You can take your time and consider exactly how much you want it, where you are, and what the floor looks like. Perhaps it will have picked up something else from the floor and won’t taste as good as you thought. Or perhaps the additional time will allow you to consider your embarrassment as you explain your behavior to those around you.

This entry was posted on April 17, 2007 at 10:22 pm and is filed under Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response or trackback from your own site.