Asthma and allergies: proof of a protective “dog effect”?

Actu GP Asthme et allergies : la preuve d’un « effet chien » protecteur ?

As Brigitte Bardot said, “a dog, a cat is a heart with hair around” … and bacteria inside, one might add.  How could exposure to pets early in life benefit us?


According to a growing number of studies, certain bacteria could benefit the children of dog and cat owners: exposing them at a young age to one or the other of our four-legged friends is thought to strengthen their immune system. This is the “microbiota hypothesis”, which has not yet been fully accepted among the scientific community. By characterizing the changes instigated by a dog in the domestic microbial environment, a new study provides ammunition for this theory, and for dog lovers.

A robust protocol

American researchers recruited 27 families about to adopt a dog, and 27 others who did not possess a dog or other fur-bearing animal. The crucial part of the study consisted in collecting dust samples a few days after the arrival of the dog, then a year later, following a fully robust protocol: first, in the room where residents spent most of their time, a prefabricated rectangle of one by two meters was vacuumed for two minutes; then the bag was changed and all the surrounding area were vacuumed, not forgetting the skirting boards, corners, furniture (on top and underneath).

A “dog effect” that is still poorly defined

From the first weeks in their new homes and up to a year after their arrival, the dogs effectively increased the diversity and levels of certain species in the domestic bacterial environment, including some species which are associated with a lower risk of developing asthma and allergies. For the children, this would be mean a stimulated immunity, an essential parameter which should be confirmed by other studies. But there are many remaining questions regarding this protective “dog effect”: which bacteria or combinations of bacteria are involved and how do they impact the intestinal flora of children? Do they come from the dogs themselves or from the external environment, like “hitchhiking” bacteria clinging to dog hair? Which type of fur—and therefore breed—should be favored? Many other dust aspirations will be needed to clarify this.  Cat owners can be reassured: a positive “cat effect” was also observed in other studies. So, get on and adopt…



AR Sitarik et al. Dog introduction alters the home dust microbiota. Indoor Air 2018; Feb 22