Are you having an allergy-free summer? You may have Fido to thank for that.

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If you’re a dog person, your kids might be in luck. Research suggests that children who grow up in homes with pets are less likely to develop allergies, and now a recent study by researchers from the University of California, San Francisco, sheds some light on why.

Working with mice, the scientists found that exposure to house dust from homes with a pet appeared to protect the mice against a common virus called respiratory syncytial virus (RSV), which infects the lungs and breathing passages and is a major cause of respiratory illness in young children. (In adults, it usually causes run-of-the-mill cold symptoms.) Severe infections in infancy are linked with an increased risk of developing respiratory problems like asthma later on.

Lead researcher Kei Fujimura and her team looked at three groups of mice. One group was fed house dust from homes with dogs, and then exposed to RSV; a second group was infected with RSV without exposure to dust; and a control group of mice was not exposed to RSV or dust.

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The study found that the mice that ingested house dust and were exposed to RSV didn’t develop the telltale symptoms of infection, such as lung inflammation and mucus production — these animals looked just like the controls. The researchers then examined the microbes living in the protected animals’ guts, and found that the types of bacteria they harbored were different and more diverse than the bugs in the RSV-infected animals guts.

What do gut bugs have to do with asthma? Potentially a lot. Researchers are discovering that the microbiome, as it’s known — the vast community of good bacteria and viruses that live in and on the human body, including in the intestines — not only play a vital role in basic bodily functions like digesting food, producing vitamins and fending off infection, but may also contribute to the development of chronic conditions and diseases like obesity, cancer and asthma.

Our bodies begin to acquire these crucial microbes at birth, during our journey through the birth canal. From that point, exposure to everything — from grandparents to pets — influences the makeup of the microbiome. It’s theorized that microbial exposure in infancy, when the immune system is maturing, may help protect children against later allergies and asthma.

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In earlier work, Fujimura found that house dust from homes with cats and dogs had significantly different types of bacteria than dust from homes without pets. And previous studies have suggested that early life pet exposure and ownership is associated with reduced risk of asthma. “This led us to speculate that microbes within dog-associated house dust may colonize the GI tract, modulate immune responses and protect the host against an asthmagenic pathogen, RSV,” she said in statement about the study, which was presented at the annual meeting of the American Society for Microbiology in San Francisco.

The findings support the hygiene hypothesis of allergy and asthma development, which posits that exposure to germs in childhood helps strengthen the immune system, reducing the risk of childhood respiratory and allergic diseases. Studies have shown, for instance, that kids who grow up on farms and around livestock are less likely to develop asthma and allergies than those who live in more sterile urban environments.

“Everybody appreciates the fact that we’re all missing something big in asthma,” Dr. Robert Mellins, a pediatric pulmonologist at Columbia University, told ABC News. “People have appreciated that viral infections clearly have an association, and this kind of experiment is interesting because it suggests a mechanism of how that could come about.”

Fujimura concludes that identifying the specific species of microbes and the precise mechanisms that underlie the protective effect of dog-associated house dust could help researchers better understand and treat allergies and asthma.

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