The Three Second Rule or the Five Second Rule

Since the 1950’s people who have accidentally dropped food on the floor have immediately invoked the infamous three second rule (or its variant, the five second rule). By immediately shouting “three second rule” individuals hope that, like some foodie exorcism, it shocks teeming bacteria into a temporary paralysis, preventing contamination of the food item within this brief window of time. Of course, germaphobes (you know who you are) would never attempt such a shocking salvage expedition, and quickly walk away from the food fumble. Interestingly, in a survey conducted by the University of Illinois at Urbana-Champaign, 70% of women and 56% of men were well-versed in this rule; and the women were more likely to invoke it than men.

The veracity of the three second rule, or the five second rule, has been the subject of many lab tests over the years, each adding layers of knowledge to this time-honored rule. The most recent study, in May of 2012, by the researchers from Manchester Metropolitan University (MMU) in England provides a summary of what has been learned:

1. The moment an item is dropped on the floor it picks up whatever bacteria is present; length of time on the floor is not a critical factor.
2. How contaminated a surface is when the food falls is the critical factor: of all surfaces, carpet presents the best breeding ground for bacteria. 
3. Dropped dry processed foods with a high salt or sugar content, and low moisture, tend to pick up less bacteria than food that is high in moisture and has low levels of salt or sugar.

The researchers recommended that kitchen floors be mopped at least once a day and that mop heads get replaced every three months. Women participating in the test, recommended that the researchers get a reality check and consider themselves lucky for not being struck on the head with a mop for setting such unrealistic standards for a busy household — especially one with kids.

For further reading: Because I Said So! by Ken Jennings, Scribner (2012)


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