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Should We Let Them Eat Dirt?

Published on Psychology Today

The “5-second rule” is that unwritten law that makes it socially acceptable to eat food off the floor if it’s only been sitting there for 5 seconds or less. The idea behind the rule is presumably that we have 5 seconds before the dropped food gets infiltrated with bacteria and becomes potentially harmful to eat. I used the rule a lot growing up, but I use it even more now that I have a 2-year-old son who is constantly dropping food on the floor—food that he will eat if I don’t scoop it up first.

To my dismay, researchers from Rutgers University recently showed that the 5-second rule doesn't do much to protect you from ingesting bacteria. The researchers tested the validity of 5-second rule by dropping different types of food onto different types of surfaces to see how long bacterial transfer would take. Not surprisingly, they found that the longer food stays on the floor, the more bacteria gets transferred to it. But (and this is a big BUT), some bacteria gets transferred to the food as soon it hits the ground, even if the food only stays there for less than a second, suggesting that the 5-second rule doesn’t actually buy much in terms of avoiding contamination.

At first, this finding might make you think twice about eating food that’s fallen on the floor. But the underlying assumption behind the 5-second rule is that the bacteria ingested from the floor are somehow harmful to your health. It turns out that most of the time, they aren't.

Recently, a group of researchers from the University of British Columbia published a book called “Let Them Eat Dirt.” The title of the book is pretty clear about it’s main point: It’s healthy for children to play in the dirt, and it may even be healthy for them to eat it. In the lab, these researchers studied the amount of bacteria babies had in their bodies, and the relationship between ingesting these bacteria and getting sick. Surprisingly, they didn’t find that contact with bacteria necessarily caused children to get sick; instead, they found that 3-month-old babies who had more unique types of bacteria in their bodies were less likely to develop allergies like asthma several years later. To explain these results, the researchers argue that maintaining contact with different kinds of bacteria can help children to build healthy immune systems.

This view might sound weird, but it’s been echoed in recent concerns about the effects of substances like antibacterial soap on children’s health. In fact, the FDA recently banned several of the antibacterial chemicals used in soap, suggesting that anti-bacterial soaps might do more harm than good. It does turn out that the vast majority of the bacteria we encounter on a day-to-day basis are perfectly safe, and according to the authors of “Let Them Eat Dirt,” may even be good for us.

So should we let our children eat dirt? There are some rules of thumb we can take from this research to help us keep our children healthy, while at the same time, not going overboard with cleanliness so that we inhibit children’s enthusiasm for playing outside or prevent them from getting exposure to benign bacteria that can help build healthy immune systems.

First, yes, let them get dirty. Playing outside is something children do less now than they did in the previous generation, and encouraging them to play in the backyard is probably good for their health and general well-being. But, not all environments are created equal. Although most bacteria are completely safe, there are some forms of bacteria that are likely to get us sick, like the bacteria found in feces or urine, or the bacteria that cause illnesses like Salmonella. Unfortunately, epidemiological studies suggest that these bacteria are most commonly found in areas like daycare centers and playground equipment. In fact, there was a Salmonella outbreak in Australia in 2007-2009 that researchers say likely resulted from ingesting playground sand.

Bacteria that cause Salmonella can also be found on kitchen floors, as a result of splatter from opening containers of raw food. Surprisingly, according to the study on the 5-second rule, rugs and carpets don’t transmit as much bacteria as surfaces like stainless steel or wood. In fact, kitchen floors might be particularly risky breeding grounds for bacteria. While I’m sure we all do a great job of keeping our kitchen counters clean, some of the food-related bacteria that we wipe off inevitably land on the floor. And it’s the food-related bacteria that come from raw meat that could have the most negative effects on health.

So there’s nothing wrong with letting our kids get a little dirty. They can even eat a little bit of dirt or food that’s fallen on the floor once in awhile, as long as it’s not off the kitchen floor, and as long as it’s not from public places like playgrounds that attract a lot of kids. In the end, all children are going to get sick from time to time, but hopefully getting a little bit dirty now and then can help them fight off future illnesses; and maybe they can even have some healthy old-fashioned outdoor fun along the way.

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