Dogs share our indoor spaces, but their impact on the air has been difficult to measure. New findings begin to map how their presence influences particles, gases, and microbes indoors.
We spend an estimated 90% of our time indoors, yet regulations and guidance around indoor air quality remain limited. Air inside buildings is shaped by ventilation and by a wide range of indoor sources, including building materials, furnishings, heating and cooking, fragrances, and personal care products. People themselves are also a significant source of indoor emissions.
We are constantly shedding skin, hair, oils, and microbes, while also releasing carbon dioxide, ammonia, and volatile organic compounds (VOCs) through metabolism and everyday activities. Indoors, these emissions can interact with oxidants such as ozone to form secondary particles and gases that have been linked to respiratory irritation and other health concerns, especially among vulnerable populations.
Dogs share these environments with us, often spending much of their time inside. They have been proposed as potential sentinels for environmental health because they share our exposures to air, water, food, and household chemicals. Yet despite their ubiquity in homes, the contribution of dogs to indoor air chemistry and microbial exposure has remained poorly quantified.
In the dog house
To address this gap, a multinational team of scientists set out to systematically measure the chemical, particulate, and microbial emissions from dogs under controlled conditions, and to examine whether body size plays a role. Using a climate chamber, the researchers measured gases, particles, and airborne microbes emitted by groups of small and large dogs, comparing those emissions with measurements from human occupants alone.
The study, published in Environmental Science & Technology, revealed clear size‑related patterns:
- Larger dogs emitted carbon dioxide and ammonia at rates comparable to a seated adult human and substantially higher than small dogs.
- Both small and large dogs released more airborne particulate matter than humans, particularly in the coarse size range (1–10 micrometers).
- Small dogs, which were generally more active during the experiments, produced the highest particle emissions overall.
Dogs were also important contributors to indoor microbial air. Larger dogs released two to four times more airborne bacteria and fungi than their owners, and the presence of dogs shifted the composition of airborne microbial communities toward greater richness and diversity. Many of the detected microbes were associated with outdoor environments, supporting the idea that dogs act as mobile carriers, transporting particles and microorganisms between outdoor and indoor spaces.
The researchers also examined VOC emissions under low‑ozone and elevated‑ozone conditions. When ozone was present, a broader range of oxidized VOCs appeared in the air. However, dogs emitted fewer ozone‑derived products than humans, likely reflecting differences in skin oil composition. Human skin contains squalene, which readily reacts with ozone to form volatile products, whereas canine skin oils lack this compound. The authors suggest that some observed VOCs may arise from human skin oils transferred to dog fur through petting — a hypothesis consistent with the chemistry but not directly tested in the study.
What does this mean for indoor spaces?
Taken together, the results show that dogs can contribute meaningfully to indoor air chemistry and microbial exposure, sometimes at levels comparable to humans, depending on dog size and activity. While the health implications of these exposures remain uncertain, the findings suggest that pets are an important (and often overlooked) component of indoor environments.
The authors argue that future indoor air quality models, ventilation strategies, and exposure assessments should explicitly consider pets alongside human occupants. Doing so could lead to more realistic approaches to managing indoor environments — not just for people, but for the animals that live with them.
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