Forget the '5-second rule' — a geneticist says any new parent should 'roll their child on floor of the New York subway'

Erin Brodwin
Business Insider
Subway Pants 7
Subway Pants 7

(REUTERS/Carlo Allegri)
You've probably heard about the five-second rule. You've probably also heard that it's not a real thing. Basically, no matter how hastily you snatch up that delicious donut from its unfortunate position on the pavement, it'll ultimately pick up a bunch of bacteria from the ground.

Here's the good news: In the vast majority of cases, bacteria isn't deadly. In fact, some studies suggest the opposite is likely true. Yes, coming into regular contact with the germs in our environment can actually be good for us!

Dr. Aaron E. Carroll, a professor of pediatrics at Indiana University School of Medicine, took up the case in a recent op-ed for the New York Times which he titled, "I'm a doctor. If I drop food on the floor, I still eat it."

Carroll's take-home message is simple. We interact with so many dirty, truly germ-infested objects every day — from grimy toilet handles to grungy cash — that trying to avoid certain surfaces is utterly pointless. "For most of us, our immune systems are pretty hardy. We've all been touching this dirty stuff for a long time, without knowing it, and doing just fine," he writes.

Many scientists have taken Carroll's thinking a step further. Their research suggests that instead of being merely harmless, regular contact with everyday bacteria can actually be helpful.

According to an idea called the hygiene hypothesis, exposure to germs and certain infections helps prime the immune system so it can defeat these microbes more easily in the future.

Research suggests the most important time for this exposure is during childhood. The idea could partially explain why children who grow up around animals and in rural areas appear to develop conditions like asthma less often than children who don't, though more studies are necessary.

And even for people other than young children, the hygiene hypothesis makes intuitive sense: After all, literally every surface in the world is covered in bacteria. The idea that things can be "perfectly clean" is a myth — humans need bacteria to live.

"We tend to think of our homes and personal environments as these pristine places, and public ones as dirty and infested with bacteria," Chris Mason, a Weill Cornell Medical College geneticist and the author of a study looking at all the bacteria on the New York City subway, said at a 2015 event in Manhattan. "But you should really think of yourself as a rabbit who gets to hop between two forests."

That's why Mason isn't afraid to let his own young daughter ride the subway or play in the dirt.

"I would advise any new parent to roll their child on the floor of the New York subway," said Mason.

Like the surfaces people touch and the ground they walk on, the human body is already teeming with thousands of different species of bacteria, from the Lactobacillus acidophilus lining digestive tracts to the Propionibacterium acnes populating the skin on faces and arms. On average, about three pounds of our body weight is accounted for by bacteria alone.

So the idea that a little more exposure couldn't hurt makes sense. Perhaps, then, everyone could afford to be a tiny bit less germaphobic.

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