Do you follow the “five-second rule?” The rule, a mostly-unscientific bit of urban legend, has been handed down through the last few generations as an acceptable metric for the length of time a dropped food item could touch the floor, for example, in your dining room or kitchen, and still be considered OK to pick up and eat. Those of us with dogs may find the rule overruled by the “half-second rule” measuring the time we have to grab the food before our pets do, but that may turn out to be for the best, and here’s why. Researchers at Rutgers recently put the five-second rule to the test.
The Rutgers study, Longer Contact Times Increase Cross-Contamination of Enterobacter aerogenes from Surfaces to Food, published in the journal Applied and Environmental Microbiology, evaluated four different types of food (watermelon, bread, bread and butter, gummy candy) and four different floor surfaces (carpet, wood, ceramic tile, stainless steel) contaminated with Enterobacter aerogenes. They also used four different durations: less than one second, five seconds, 30 seconds and 300 seconds. Contamination levels were measured for each food after each test.
The results showed the expected relationship that longer durations of contact resulted in more contamination, but the type of food and the contact surface also showed differences. Watermelon generally became the most contaminated – the high moisture content made it easy for bacteria to transfer to the food surface. Gummy candy picked up the least bacteria. When it came to surfaces, the carpeting had the lowest transfer rate, while tile and stainless steel transferred more. Results for wood were somewhat variable. While carpeting might intuitively sound “dirtier” to many of us, its fibrous nature enables bacteria to stick to it – likely disadvantageous long-term as bacterial colonies build up, but in a single test, it was more difficult for bacteria to leave the carpeted medium.
The researchers summarized that the five-second rule was a “significant oversimplification” of scientific research. The reality is far more nuanced, impacted not just by what was being eaten but also where it was dropped. In fact, the researchers found that some transfer takes place “instantaneously” (at times <1 second). While most who subscribe to the five-second rule were already aware it wasn’t truly backed by science and was more of a heuristic we could use when we really didn’t want to re-make our toast, studies like this are a fascinating way to confirm what is myth and what is reality.
Studies like this also speak directly to us at Xenex, where we research the dangers of contaminated high-touch surfaces in hospital rooms – which are often made of tile and stainless steel, like the high-transfer surfaces in this study – and the potentially lethal bacteria that can remain after standard cleaning. To learn more about UV disinfection and how our Xenex LightStrike™ Germ-Zapping Robots™ kill the germs on surfaces, check out our research and results