Asthma rates are on the rise. The incidence of this respiratory disorder, which occurs when air passages become chronically inflamed and narrowed, has shot up by more than 20 percent in the past two decades.

It's now estimated to affect some 25 million people in the U.S., with children suffering from it the most.

The precise cause of the increase—and indeed, of asthma itself—is unknown.

But mounting evidence suggests that being exposed to certain bacteria at an early age may reduce a youngster's asthma risk, says B. Brett Finlay Ph.D., a microbiologist at the University of British Columbia in Vancouver.

His research suggests that the trillions of bacteria, fungi, and viruses that line our skin and digestive tracts—called the microbiome—may play a role in shaping the immune system of children.

“Asthma is a very prevalent disease in our society now, which wasn’t the case 50 years ago,” Finlay says, who spoke on the topic at the recent meeting of the American Association for the Advancement of Science (AAAS). “We now realize that the microbes [you’re exposed to early in life] seem to set you up—or not—for asthma.”  

Although research in this area is still preliminary, children who were born by C-section, fed formula instead of breast milk, or treated with antibiotics at an early age, as well as those who live in urban, rather than rural, areas, may be more likely to develop asthma.

All of these factors, Finlay says, may limit a child’s exposure to healthy microbes.

Today, on World Asthma Day, here's what you need to know about this emerging line of thinking about asthma—and how it may help your child.

A Bug a Day May Keep The Inhaler Away

In 2012, Finlay and his team found that if you wipe out a young mouse’s intestinal bacteria with antibiotics, it's much more likely to develop asthma.

To see how the relationship between bacteria and asthma might play out in people, Finlay and his team compared fecal bacteria in 319 children enrolled in the Canadian Healthy Infant Longitudinal Development Study—a long-term research project that's been looking at the development of 3,500 children born after 2010.

The team found that the infants who harbored four types of bacteria in their guts at 3 months of age were less likely to develop asthma than those who did not. They published these results in the journal Science Translational Medicine in 2015.

“If you had them [the bacteria], you were basically protected against asthma,” says Finlay. “If you didn’t have them, you had a very high risk of asthma.”

This and other studies, says Finlay, hint that there may be an important early window when infants need exposure to certain microbes—to strengthen their immune systems and tip the balance away from the development of asthma.

Finlay believes that because we’re so focused on cleanliness, we’ve lost an essential part of our biology: healthy microbes.  

“We are suffering from a hygiene hangover,” says Finlay. “We are not getting the microbes that our grandparents got.”

As a result, he says, we’re contracting diseases we wouldn’t have 100 years ago.  

Strengthen Your Child's Microbiome

Once a child develops asthma, there's not much you can do to reverse it. That's why, says Finlay, it may be important to put certain practices into play early on in a child's life.

In his book, “Let Them Eat Dirt,” (Algonquin Books, 2016) Finlay outlines tips for increasing a child's exposure to healthy bacteria.

Such exposure, he says, is most important between birth and age 2. But all of the strategies below can be employed throughout childhood, and may help mitigate the risk of not only asthma, but other diseases linked to an unhealthy microbiome, including allergies, inflammatory bowel disease, and obesity. 

“It’s fascinating, and there’s a lot more to learn,” says Jay Portnoy, M.D., director of allergy, asthma, and immunology at Children’s Mercy Hospital in Kansas City.

Portnoy cautions, however, that the link between asthma risk and the microbiome is still not fully understood.

“We don’t know whether changing the microbiome makes any difference for asthma,” he says.

In addition, asthma can have other triggers, including exposure to allergens such as dust and pollen.

While these tips aren't a surefire way to prevent asthma, early research suggests they may help, and with basic precautions, can be safely incorporated into a healthy lifestyle.

1. Let your child play in the dirt. Mud, plants, insects, and dirt are teeming with healthy microbes.

2. Get a dog. Assuming, of course, no one is allergic, studies show that people who live with a dog have a 20 percent decreased risk of developing asthma, says Finlay.

3. Chuck the antibacterial soap. Antimicrobial soaps and gels may seem like a smart idea, but they’ll destroy the beneficial microbes your child has picked up. Washing with regular soap and water is enough; and the only time your kid’s hands need to be squeaky clean, says Finlay, is before a meal and after using the bathroom.

4. Feed their microbes. Like humans, microbes need to eat to stay healthy. And they prefer high-fiber, nutritious foods like nuts, legumes, and vegetables, as well as fermented foods such as yogurt and kefir.

5. Use antibiotics sparingly. These drugs can be important for serious bacterial infections, but when they’re unnecessary—for colds or other viral infections, for example—skip them. They “carpet bomb” both good and bad bacteria, as Finlay says, dramatically disrupting the composition of microbes in your body.  

The asthma risk of a child born today is much higher than it was in the past. The disorder, which results from chronically inflamed air passages triggered partly by an overactive immune system, has shot up in prevalence by more than 20 percent in the past two decades. It's now estimated to affect some 25 million people in the U.S., with children burdened most.