Dear Doctor: Neither of my sisters have pets, and all their kids have allergies. Could the fact that we have dogs, a horse and a barn cat be the reason that my kids aren’t allergic to anything?
Dear Reader: How and why allergies develop are complex questions that have long been the subject of study. So many variables are at play, both genetic and environmental, that it’s difficult to pinpoint why someone does develop an allergy and someone else does not.
That said, an emerging body of evidence suggests that early exposure to pets may indeed offer a measure of protection from developing an allergy. It’s tied into what we’re now learning about the importance of the gut microbiome, which is the array of microbes and microorganisms that coexist within our bodies. This insight offers new avenues of research and understanding that are both fascinating and intriguing.
Let’s back up and talk about what, exactly, an allergy is.
An allergy develops when the immune system perceives a normally harmless substance as a threat and then mounts a vigorous defense against that substance. Dust mites, pollen, certain foods and pet dander are among the substances that the immune system may suddenly begin to target. The result of this hypersensitivity can manifest as itchiness, swelling, hives, wheezing, difficulty breathing, stomach upset and vomiting. Most allergies are manageable and are merely unpleasant or annoying. However, some allergic reactions can be so extreme that they are life-threatening.
The original idea behind the pets-are-good theory of allergy protection was that, through early exposure, individuals became desensitized to the presence of potential allergens. New research now suggests a connection between regular contact with animals and beneficial changes to the gut microbiome.
Some researchers believe that when a child is exposed to certain pet-associated microbes, the result is a beneficial effect on the development of his or her immune system. The theory is that the presence of animals adds a level of diversity to the microbes that the child encounters daily. The result is an immune system that’s measurably less trigger-happy in the presence of potential allergens.
However, this exposure appears to be at its most effective before birth and during the first 12 or so months of life.
What’s also interesting is that stool samples taken from children who grew up on a farm, and therefore came into regular contact with a variety of animals, had a broader diversity of microbiota than did samples from children living without pets. And it’s not only contact with the animals themselves that scientists believe has benefits. The microscopic traces of soil that cling to the animals and get transferred to people, or that the animals bring into the home, contribute to an environment with a more robust and diverse array of useful microbes.
With research into the mysterious and fascinating microbiome still in its infancy, we can only imagine the revelations to come.
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Eve Glazier, M.D., MBA, is an internist and assistant professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and primary care physician at UCLA Health. Send your questions to firstname.lastname@example.org, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.