In 2015, Canadian microbiologists Marie-Claire Arrieta and Brett Finlay made an important discovery when studying the connection between gut health and childhood asthma. They noticed that babies who were missing four key microbes—miniscule, oblong organisms that primarily live in our guts—often went on to develop asthma. “This was startling for us, not just as microbiologists but as parents,” says Arrieta.

The duo wrapped up their study, then did a massive review of scientific literature on microbes—collecting, analyzing, and translating research. They consolidated their research into the book, Let Them Eat Dirt: Saving Your Child from an Oversanitized World, lauding dirt and a host of other microbe-rich specimens as capable of bolstering your child’s long-term health.

“Microbes cover everything,” says Arrieta, and humans are constantly relying on microbes. Some train our metabolisms; others fine-tune our immune systems. Microbes even help drive our nervous responses. Occurring in all sorts of interesting shapes and sizes, microbes are efficient, resilient entities. “They can stay dormant for years, then come back to life,” says Arrieta, adding that the critters look pretty neat under a microscope, which is what you”ll need in order to see them.

Individual microbe cultures live together in large communities called microbiota, and, continues Arrieta, ‘they existed way back before there were large living things like humans.” In fact, Finlay interjects, “it was throughout the evolution of microbes that we came about.”

Goodbye, Microbes

“Over the last hundred years, we’ve worked like crazy to clean up our world,” says Finlay. With cleaner food and water, vaccines, and antibiotics, it’s rare, now, for a child to die from infection. But, warns Finlay, “In our quest to get rid of all infectious microbes, we’ve gone too far.”

While researching lifestyle choices for chapter nine of Let Them Eat Dirt, Finlay and Arrieta discovered there is such a thing as too clean. They heard from parents who disinfect baby toys with bleach and sanitize floors before letting toddlers crawl. Keeping your house as clean as an operating room isn’t necessary; and, it’s potentially harmful. It robs young children of the microbes they should be ingesting for health.

How Kids Get Microbes

In utero, babies don’t have a single microbe. A microbe-bath happens at delivery, when infants emerge and ingest millions of microbes in mere moments. “Vaginas—which are really close to where feces come out—are just packed with microbes,” explains Arrieta, calling birth “a dirty, bacteria-rich process.”

With medical advances, though, some mothers are inadvertently depriving their children of a pivotal opportunity to ingest microbes by scheduling Cesareans that aren’t medically necessary. In 2014, for example, the Centers for Disease Control and Prevention reported 32.2 percent of American babies were born by C-section—more than double the rate the World Health Organization recommends. “If a baby doesn’t come out of the vagina, it will still be bathed in other microbes,” Arrieta clarifies. “But not the most healthful ones.”

A baby’s next opportunity to “eat dirt” comes at feeding time: “Breast milk is packed with microbes,” says Arrieta, noting that microbes on a mother’s skin are also transferred during mealtime. Formula-fed babies, Arrieta explains, miss both of these transfers.

“The first year of life is the most important for establishing the microbes you”ll live with forever,” continues Arrieta. Toddlers are preprogrammed to eat microbes as they explore the world in their hands-on way, unabashedly touching surfaces and people. Arrieta and Finlay ask parents to refrain from interfering with a child’s natural instinct to touch. They encourage parents to let their children play freely in sandboxes, creeks, and the woods.

“Parents should relax,” Arrieta says. If a pacifier lands on the floor, pop it in your mouth and hand it back. Don’t panic when your daughter touches the filthy underside of a restaurant table. “What we”re trying to do is promote a healthy exposure to microbes,” Arrieta says. “Promoting healthy microbes is different than intentionally exposing kids to disease.” Neither doctor recommends letting your kiddo, say, lick the floor of a New York subway station. “And certainly don’t shovel dirt into a newborn’s mouth,” Finlay adds.

Other Ways To Prevent Disease

Preventing disease with common sense and vaccines is every bit as important as feeding children microbes. With one caveat, that is: Over-the-counter antibacterial hand soaps are a big microbe no-no. The FDA recently ruled against them, questioning both safety and effectiveness.

Wash up with regular soap and water before dinner, but don’t worry about washing your child’s hands a hundred times a day, says Finlay. He and Arrieta call for restraint with antibiotics, too, which kill good and bad bacteria at the same time.

“Antibiotics are a wonder drug when used right, but we have to be smarter about how we use them,” says Finlay.

In our over-sanitized nation, many children struggle to eat—and keep—the microbes their bodies need, and the result has been an increase in the incidence of Western lifestyle diseases: asthma and allergies, obesity, inflammatory bowel disease, diabetes, and behavioral and mental health disorders, covered in Part III of Let Them Eat Dirt.

Sustaining Your Microbes

Worried your child might be microbe deficient? Don’t be. There’s still time to introduce new microbes while positively influencing the existing ones, too.

“Diet,” Finlay explains, “is a hugely important component.” White sugar and flour—staples in many conventional kid foods—might quell your child’s appetite, but they”re failing to sustain his or her microbes. “You have to feed your microbes,” Finlay says. A few microbe friendly alternatives include raw fruits and vegetables, whole grains, and fermented foods, such as yogurt, kefir, pickles, sauerkraut, and kombucha.

Probiotics are another source of easy-to-ingest microbes. In fact, pharmaceutical companies are currently developing new-generation medical probiotics—pills, most likely—that might be available in the next five to 10 years, says Arrieta.

In the meantime, canine-lovers can stock up on microbes at home. “Dogs drag in a ton of dirt from outside on their paws, and they lick your kid’s face,” Finlay says. Owning a dog is the next best thing to living on a farm, and, Finlay adds, will decrease your child’s chance of developing asthma by about 20 percent. Sorry, cat people, but the principle doesn’t hold for other furry companions.

If you’re ready to start “eating dirt” with your family, grab a copy Finlay and Arrieta’s book. Read it in the mountains while your children run around, and stock up on any microbes they might be missing.

5 Ways to “Eat Dirt” Locally

• YMCA of the Rockies” Snow Mountain Ranch: From horses to hiking, this family friendly destination is a premier place to collect microbes and memories. snowmountainranch.org
• Denver Botanic Gardens: Designed to resemble a secluded mountain hideaway, the Mordecai Children’s Garden is an urban microbe oasis. botanicgardens.org
• Children’s Museum of Denver Joy Park: Kids dig in to water, sand, dirt, and straw at this park for fun and learning. mychildsmuseum.org
• White Fence Farm: If you can’t live on a farm, play on one before indulging in a hearty, 100 percent dirt-free dinner at this beloved mainstay. whitefencefarmco.com
• Noosa Yoghurt: Microbes have never tasted so good. Grab a spoon, a tub of thick and tangy Colorado yogurt, and enjoy. noosayoghurt.com
• Rowdy Mermaid Kombucha: Ditch the soda for a fermented, effervescent, microbe-laden beverage manufactured with Colorado snowmelt in Boulder. rowdymermaid.com