The Five-Second Rule

A piece of food falls to the ground. Can you eat it if you pick it up immediately? The common belief is that you can—supposedly, there’s a brief grace period, a typically five-second window (though some people estimate the time to be as long as ten seconds) when you trust that your wayward morsel will be safe from contamination with floor germs.

This is not strictly true. In a pioneering study, a researcher in Chicago found in 2003 that not only does contamination not hold off for five seconds, it actually almost all happens within that time. A later experiment, on the television show Mythbusters, showed that food is almost as contaminated after two seconds as after six, meaning most microbes that attach themselves to food do so immediately. Even a split-second of contact is enough to start the process.

There is a bright spot, however. The 2003 research used floor tile covered in bacteria, an intentionally engineered worst-case scenario. Tests carried out in more natural environments got more optimistic results; while contamination of food is faster than many people had believed, floors, even in public places, proved cleaner than many people suspected.. When the floor is already clean, there is little danger in the short term, though tile is still a safer bet than carpet. Carpet carries the additional danger of fibers in the food, and not the kind you want. Another test on another television show found that high-traffic floors are worse for food, and a South Carolina study—a class project at Clemson University in 2006—found that bacteria can survive on a floor for a month.

This also has interesting implications for children’s health. At least one website recommends boiling baby pacifiers and teething devices that fall on the floor, regardless of how briefly. However, this may doom your child to serious illness later in life. One widely accepted explanation for many autoimmune diseases is called the hygiene hypothesis, It says that when children are exposed to dirt and microbes, this trains the immune system, helping it recognize what’s a legitimate threat. Children raised in clean environments don’t have these experiences, and so the confused immune system attacks the body’s own tissue.

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