Myths and Misconceptions: The Three Second Rule

Being a child is awesome. You get to spend most of your time pretending you’re a dinosaur or fairy or Harry Potter, there’s none of this “study” bullshit and possibly best of all, there’s no shame in eating food that you accidentally dropped on the ground. However there comes a time in all of our lives when eating that chip from down the back of the couch becomes socially unacceptable. Luckily, all hope is not lost; the “three second rule” is the perfect justification for the piece of toast that tumbles from the table buttered side down. According to this widely-practiced principle, it’s safe to eat food that’s been dropped on the floor, so long as it’s retrieved within three seconds.


Presumably, any more than three seconds and the itsy bitsy bacteria will have contaminated your food. Shockingly, I’ve heard some people abide by a five second rule – what disgusting monsters! Their food must be crawling with all kinds of nasties! But seriously, does two extra seconds make that much of a difference? In fact, these seemingly arbitrary timespans raise an important question: is there actually any scientific merit to the three (or five) second rule?


Last year, scientists tested out the golden rule of human food consumption, using five different food items. Each item was dropped on the floor and left for three, five and ten seconds, then the growth of bacteria was examined. Sugary and salty items – like ham and bread with jam – fared well as bacteria find it tough to survive in such conditions. Similarly, biscuits showed minimal bacterial growth because their low water content means it’s harder for bacteria to stick to them. Dried fruit and cooked pasta, however, did display some bacterial growth.


This isn’t the first scientific study into the three second rule phenomenon: Jillian Clarke received the Ig Nobel Prize in 2004 for her work in this area. Her findings indicated that minimal contamination of food occurred when dropped on a public floor. Following this pioneering work, further investigation revealed that bacteria can cling to food within just five seconds of contact, while contact times of more than a minute increased the number of bacteria present.


Other experiments, including some performed by TV programme Mythbusters, found that contact time did not significantly increase the number of bacteria contaminating a food item. Instead, the moisture or stickiness of a foodstuff largely determined whether it became contaminated. The surface geometry and where the food was dropped also had a notable effect.


But just because you get a few germs relocating to your food if it’s dropped on the floor, does this mean the levels of contamination are high enough to cause illness? Probably not. It’s not healthy to avoid all bacteria at all costs, but I wouldn’t recommend salvaging an ice cream that’s plummeted to a dirty demise either. Just use your common sense when applying the three second rule. It may not be scientifically justified, but if it makes you feel better about rescuing a delicious piece of fallen chocolate then I say go for it.



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