Do you want your child to have fewer allergies? Having a dog in the home may help.
New research shows that 56 different classes of bacteria are “significantly more abundant” in houses with dogs. Combined with a prominent 2016 study that showed children who grow up with farm animals near their homes have lower rates of allergies and asthma, and some immunologists are concluding that dogs likely lower children’s risk of allergies.
The idea comes from a branch of research around the hygiene hypothesis, the theory that people in developed countries have higher rates of allergies and asthma because they’re exposed to fewer germs.
Children from the U.S. and other developed countries are significantly more likely to develop allergies, and the number of Americans with allergies has skyrocketed since the 1970s. It has continued to increase in recent years.
A lot of other evidence supports the hygiene hypothesis. In the 2016 study, researchers looked at the differences between Amish children in Indiana — who have very low rates of allergies and asthma — and Hutterite children in North Dakota, who have much higher rates of both.
At first, they seem like similar populations, since both are insular farming communities. They also have similar diets, lifestyles and genetic backgrounds, with the Amish originating in Switzerland and Hutterites originating in Austria.
But there is a major difference: The Amish live on small, single-family farms with barns close to their homes, and the children frequently play in the barns. The Hutterites, on the other hand, live on large commercial farms with the animals far away from the home. Hutterite children generally do not play in the barns.
The study found that the Amish had a lot more bacteria in the dust in their homes than the Hutterites. In addition, the Hutterites had a lot more eosinophils, a type of immune cell that provokes allergic reactions.
Even more stunning, when the researchers consistently exposed mice to the bacteria-filled dust from Amish homes, the mice were much more immune to allergies. When they exposed different mice to the cleaner dust from Hutterites, the mice were less protected.
A co-author of the study, Dr. Jack Gilbert, said most American children aren’t going to live on farms and be exposed to those extra bacteria, so cohabitation with dogs can serve as a proxy and help boost children’s immune systems.
“If we can’t bring our kids to the farm, maybe we can bring the farm to kids,” Dr. Gilbert told The New York Times.
Dr. Hartog said the evidence in these types of studies is compelling.
“There’s a very low prevalence of allergies and asthma in those populations when the kitchen is right next to the farms,” Dr. Hartog said. “Certainly a correlation doesn’t prove causation, but it suggests animals have an effect.”
Dr. Hartog said there are caveats when thinking about getting a dog for health purposes. First, the dogs must be allowed to roam outdoors. “Indoor dogs don’t carry the same benefits,” he said.
Secondly, some people are allergic to dogs or the various pollen that dogs track into homes. In that case, the dogs wouldn’t be beneficial. But on the whole, he leans toward recommending dogs.
“‘If you’re going by evidence, the dog is likely more beneficial’ is what I tell people when they ask that question,” he said.
Introduction to bacteria and microbes is especially impactful when it comes to children, the evidence shows. For example, kids who avoided peanuts in their first two years had a peanut allergy more than 30 percent of the time, Dr. Hartog said. But if peanuts were aggressively introduced to babies in their first year, they had less than a 1 percent rate of peanut allergy.
The current thought is that introduction to bacteria and allergens is most beneficial early in life, “when the immune system is developing and forming,” Dr. Hartog said. “Once it’s developed, there is probably less of a chance to alter it and make you immune.”
It makes sense that a dog could have a positive effect on a child’s immune system by bringing more outdoor bacteria into the house, Dr. Hartog said. Still, he cautioned that more research is needed.
“There’s a lot of instances in medicine where common sense has proven to be very, very wrong when we look at that,” he said. “But the evidence does lean toward dogs as likely beneficial.”