Dogs do more than bark, sleep, and play. A new study in Environmental Science & Technology, published online on February 1, 2026, looked at how dogs change indoor air. The team tested seven dogs in Switzerland: four small Chihuahuas and three big dogs—a Tibetan Mastiff, a Newfoundland, and an English Mastiff. The dogs stayed in a controlled room with their owners, so the researchers could check the air very carefully. (pubmed.ncbi.nlm.nih.gov)

The results were surprising. Big dogs gave off carbon dioxide and ammonia at levels close to a seated adult human. They also released much more bacteria and fungi into the air than people did—about two to four times more. Many of these tiny living things seemed to come from outside. This suggests that big dogs can bring outdoor material into the home on their fur and paws. (pubmed.ncbi.nlm.nih.gov)

Small dogs were different. They did not send out as many bacteria and fungi as the big dogs, but they released more airborne particles. The researchers think this happened because the small dogs were more active during the tests. So, in this study, small dogs seemed to make more floating dust-like particles, while big dogs changed the air’s bacterial and fungal mix more strongly. (acs.org)

This was a small first study, so it cannot explain every dog or every home. Still, it gives us an interesting message: pets are part of indoor air, just like people are. The researchers say future air systems and ventilation plans should think about pets too. That does not mean dogs are “bad” for a room. It simply means that the size of your dog may change the air around you in different ways. (acs.org)