A Moment of Science

The 5 Second Rule: Truth Or Myth?

We've all dropped a piece of food on the floor and ate it after thinking, "It's only been 5 seconds!" Is there any truth to this rule?

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Photo: Alison (Flickr)

Spilling some food, like these peanuts, may not seem like a big deal. However, no matter how long they are left on the floor for, harmful bacteria will cover the peanuts.

We’ve all heard of the “Five Second Rule” but, is there any truth to it?

Putting The Rule To The Test

In 2007, microbiologists at Clemson University put the five second rule to the test.

They coated squares of tile, wood flooring and carpet with a solution of Salmonella bacteria, waited for it to dry, and then tested how many bacteria transferred from the surfaces to food dropped on them.

After 5 Seconds

After only five seconds on the smooth tile floor, nearly 99% of the bacteria cells had transferred to a slice of bologna. Transfer of bacteria from wood floor and carpeting was lower; after five seconds five to seventy percent of the bacteria had transferred to the bologna.

Although a slice of bread picked up fewer bacteria than the bologna did, it still was contaminated with loads of bacteria after five seconds on the floor.

However, there is some truth…

The longer the bread or bologna stayed on the floor, the more bacteria it picked up, so a hasty retrieval will limit the number of bacteria that transfer somewhat.

However even a very brief contact with a contaminated floor can allow large numbers of bacteria to transfer to your food.

Why Does This Matter?

While most people with healthy immune systems are strong enough to fight off a few ingested bacteria, the infectious dose of some bacteria can be as low as ten to one-hundred individual cells.

So if you aren’t sure how clean that floor is, you may want to think twice before eating that cookie.

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