Is the 5-Second Rule True?

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

Sabrina Stierwalt, PhD
3-minute read
Episode #213

Should You Eat Food That Falls on the Floor?

Other studies have reached similar conclusions. Bacteria can be transferred immediately so a quick reaction is not going to help keep you germ free. The CDC notes germ-laden surfaces as one of the leading causes of the transfer of foodborne illnesses.

However, some researchers note that our concern over the kitchen floor is misplaced. For example, Dr. Aaron Carroll, a professor of pediatrics at Indiana University, points out that there are other surfaces in our house and even our kitchen that are far more germ-infested than the kitchen floor.

A 1998 study examined the average number of bacterial colonies per square inch on different surfaces in the kitchen. The floor turned up 2.75 colonies per square inch but that number was about doubled on the refrigerator handle (5.37 colonies per square inch) and the kitchen counter (5.75 colonies per square inch). Most people don’t think twice about eating food off of a “clean” dish, but those sponges were found to harbor 20 million colonies per square inch. Gross!

Part of the problem is that what we perceive as clean is not always really all that clean. Cell phones, for example, which we put up to our face without hesitation, are known to host more bacteria than toilet seats. We also sometimes rely on past experience to assess risk. With the first child, you may sterilize the pacifier every single time it falls on the ground, but once you know that your first kid survived just fine, and perhaps once you see just how dirty kids can get, your second child may not get the same treatment. There is even some evidence that gender plays a role, with women being more likely to adhere to the five-second rule and thus less likely to eat food off the floor.

So should we eat food that falls on the floor? Bacteria, it seems, are unavoidable so there is unfortunately no grace period for food to be contamination free once dropped on a germy surface. However, given the ubiquity of bacteria, perhaps our desire to not waste food, and our desire to avoid alarm every time our toddler eats a cheerio off the floor, are important to factor in as well. In any case, I think I’ll go scrub my kitchen counter now—and sterilize that sponge.

Until next time, this is Sabrina Stierwalt with Ask Science’s Quick and Dirty Tips for helping you make sense of science. You can become a fan of Ask Science on Facebook or follow me on Twitter, where I’m @QDTeinstein. If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.com

Photo courtesy of shutterstock.


Please note that archive episodes of this podcast may include references to Ask Science. Rights of Albert Einstein are used with permission of The Hebrew University of Jerusalem. Represented exclusively by Greenlight.

About the Author

Sabrina Stierwalt, PhD

Dr Sabrina Stierwalt earned a Ph.D. in Astronomy & Astrophysics from Cornell University and is now a Professor of Physics at Occidental College.