Have You Heard of the Five-Second Rule?


Have you ever heard of the five-second rule, where you can pick up food that has fallen on the floor within five seconds and eat it without risk of illness? Do you follow it?

I do after living in Bangkok and eating at every street vendor in the city I guess either I have a death wish or I am immune to almost any bacteria…after all consider eating an M&M after hitting my floor in Atlanta versus eating fried grasshoppers on Sukhumvit Road in Bangkok…which would have the higher health risk?

In 2003, a then science intern at the University of Illinois, Jillian Clarke, conducted a survey and found that slightly more than half of adult men and 70 percent of adult women knew about the five-second rule and many said they followed it. Clarke then conducted an experiment to find out if various food became contaminated with bacteria after just five seconds on the floor.

For performing this first test of the five-second rule, Clarke was awarded the 2004 Ig Nobel Prize in public health by the Annals of Improbable Research. Why didn’t I perform that test?

Clarke’s study inspired another research group at Clemson University to investigate several questions regarding the five-second rule: Does the type of contaminated surface affect the numbers of bacteria collected? How many bacteria does a food item collect in just five seconds? Does it collect more if it sits on the contaminated surface longer? Does it collect enough to make you sick?

To answer these questions, a Clemson team conducted several experiments of floor-to-food contamination. I won’t bore you with the details but they found that the type of contaminated surface affected the number of bacteria that the food slices took up, and the length of time that the food remained on the contaminated surface did affect the numbers of bacteria they absorbed.

Apparently, this amount of bacteria is potentially enough to cause illness in people; the infectious dose — the smallest number of bacteria that can actually cause illness — is as few as 10 for some Salmonellas.

But consider that Clarke, the original investigator, found that bacterial contamination was so low on the floor at the University of Illinois that it couldn’t be measured, unlike the levels of contamination that the Clemson group were using for their studies not to mention my living experiments in Bangkok.

So the likelihood that a cookie, quickly picked off the floor and consumed, can make you ill, is somewhat remote, but it is a factor worth considering if you are in an area where there could be significant levels of bacteria present like Soi 12 in Bangkok.