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​Our bodies contain around eight million genes. Yet only about 0.3 percent are human. The rest come from your microbiome — the sum total of genes from the numerous microbes (mostly bacteria, but also viruses, yeasts and fungi) that coat your skin, mouths, gut lining – just about everything.

Far from inert, many studies suggest your own health, and susceptibility to disease, may depend on your microbiome. And any number of lifestyle factors can influence your microbiome, things like diet, antibiotic use and even the people we live with. While a person might only have 10 percent of their microbiomes in common with a random stranger, people who live together share more microbial populations in common.

Research has even shown that you and your dog share similar microbial populations — raising questions about how your dog might affect your health, too.

You and your dog

“With a fair amount of precision, we could pick your dog out of a crowd based solely on microbiomes,” said Rob Knight, PhD, professor of pediatrics and computer science and engineering at UC San Diego.

Knight and his team found that microbial communities on adult skin are on average more similar to those of their own dogs than to other dogs. Cohabiting couples shared more microbes with one another if they have a dog, compared with couples who don’t have a dog. Dog owners in general, even unrelated and in different households, also have more microbial species in common with other dog owners than they do with dog-less people.

What do dog microbes mean for our health? According to Knight, there's mountingevidence that living with a dog in infancy lowers a child’s risk of developing asthma and allergies.

That’s probably due to what’s known as the hygiene hypothesis. Though still a matter of debate, the hygiene hypothesis is the idea that city life and all of modern society’s efforts to avoid infectious diseases — antibiotic soaps, hand sanitizer, air filters, etc. — have contributed to the rise in allergies and asthma, particularly in children living in urban communities in developed countries.

Many scientists believe that infants and children need exposure to harmless microbes in order to “train” their developing immune systems to distinguish between self and foreign molecules and not to overreact and end up damaging one’s own tissues, as immune systems do in asthma and allergies. Perhaps, as Knight’s research is finding, living with a dog helps with this immune system training.

Take part in scientific discovery

Knight and his research team are participating in two studies aimed at unraveling the complex interrelatedness of dog and owner microbiomes, and its effects — and you can, too.

Knight co-founded the American Gut Project, a crowdsourced, crowdfunded initiative in which anyone can contribute mouth, skin or gut samples from themselves, family members and dogs for microbiome sequencing. Participants get the fun of seeing how they compare to others and your microbiome information is added to a growing database that researchers can mine for potential connections between the microbiome and many factors, such as diet or living with a dog.

In a separate effort, researchers at the University of Arizona are leading a study of dogs and human health. Knight’s lab at UC San Diego is also helping out, sequencing the microbiome samples collected in Arizona. The researchers are seeking healthy Arizonians age 50 or older, who have not have lived with a dog for at least the past six months. Study participants will select a dog they would like to live with for three months and the researchers will sequence their microbiomes before and after life with the dogs. The goal of the study is to determine whether dogs enhance the health of older people by working as “probiotics.” The researchers will be separating the microbiome’s effects from other factors, like psychological benefits of living with a pet.

"The idea of combining animal, human and environmental health, and seeing the whole picture through the lens of the microbes that we share, is an increasing direction for research," Knight said in a recent interview with U-T San Diego.

Want to learn more about your microbiome and your dog’s? For more information, visit: American Gut Project

Care at UC San Diego Health

Allergy and Immunology