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23 March 2026
For most dog owners, petting their dog is second nature. A scratch behind the ears, a belly rub on the couch, or a quick pat when walking by. But according to new research, those small moments of affection may be quietly changing the air inside your home.
A recent study led by researcher Dusan Licina at the École Polytechnique Fédérale de Lausanne (EPFL) suggests that dogs can influence indoor air chemistry in surprising ways. By releasing gases, carrying microbes from outside, and even interacting with the oils from human skin, dogs may subtly reshape the air we breathe indoors.
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Dogs live in tens of millions of households worldwide, yet scientists have rarely examined how they affect indoor air quality. To explore this gap, researchers conducted the first controlled study to measure the gases, particles, and microbes emitted by dogs in a sealed climate chamber.
The results showed that dogs are not just passive occupants of indoor spaces. They actively contribute to the chemical and biological makeup of the air around them.
In the study, two groups of dogs participated: one group of four Chihuahuas and another group consisting of large breeds, including a Tibetan Mastiff, a Newfoundland, and a Mastiff. Each group spent time in a controlled indoor environment with their owner while researchers carefully measured the air.
Scientists tracked carbon dioxide, ammonia, airborne particles, bacteria, fungi, and volatile organic compounds to understand exactly what dogs release into the air.
One of the most surprising findings concerned something many owners do constantly: petting their dogs.
Human skin produces a fatty compound called squalene, which reacts with ozone commonly found indoors from outdoor air. When these substances react, they can produce new airborne chemicals and ultrafine particles.
Dogs, however, naturally contain little to no squalene in their skin oils. At first, scientists assumed dogs would not contribute to this type of chemical reaction.
Yet during the study, when ozone levels were elevated, and dogs were present with their owners, the air showed the same chemical signatures that normally appear when ozone reacts with human skin.
Researchers believe the explanation may be simple: human skin oils transfer onto dogs’ fur during petting. Once those oils are on the dog’s coat, they can react with ozone in the air, creating new airborne compounds.
In other words, every affectionate scratch or belly rub may be seeding a small chemical reaction on your dog’s fur.
The study also measured gases that dogs naturally emit through breathing and bodily processes.
Large dogs released carbon dioxide at a rate of roughly 12 liters per hour, which is comparable to a resting adult human. They also emitted ammonia at levels near the upper range typically produced by people.
Smaller dogs emitted less gas overall, but they actually released more airborne particles by mass during the study. Researchers suspect this may be due to their higher activity levels.
These findings suggest that a large dog may contribute roughly the same amount of certain gases to a room as another person would.
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Perhaps the most interesting effect involved microbes. Dogs regularly travel between outdoor and indoor environments, and their coats act like moving carriers of microscopic life.
When the dogs entered the climate chamber, the diversity of airborne bacteria and fungi increased significantly. Some of these microbes were associated with healthy dog skin, while others appeared to be environmental organisms picked up outdoors.
Large dogs released Gram-negative bacteria at about twice the rate of their owners, and their fungal emissions were also higher than those of both small dogs and humans.
Because all of the dogs had walked through the same outdoor area before the experiment, they carried similar microbes into the chamber. Once inside, those microbes entered the air and became part of the indoor environment.
Essentially, every trip outside and back in may bring a fresh set of microscopic passengers into the home.
The researchers emphasize that these findings are not a cause for alarm. The microbes detected in the study are not considered dangerous for healthy individuals.
In fact, previous research has suggested that children raised with dogs sometimes have lower rates of asthma and allergies. Some scientists believe early exposure to a wider range of microbes may help train the immune system.
However, the long-term health implications of these microbial changes remain an open question.
Current ventilation and indoor air quality standards are typically designed with human occupants in mind. Pets are rarely considered when calculating air circulation needs or emission sources.
This research suggests that pets, especially larger dogs, may contribute enough gases and microbes to influence how indoor environments should be designed and ventilated.
For architects, engineers, and public health researchers, the presence of pets may eventually become part of the equation when evaluating indoor air quality.
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If you share your home with a dog, likely, your pet is quietly shaping the air around you. Through breathing, movement, outdoor adventures, and simple interactions with their humans, dogs help create a unique indoor environment.
That doesn’t mean anyone should stop petting their dog. If anything, the study highlights just how intertwined our lives are with our pets — even at the microscopic level.
The next time your dog trots in from a walk, shakes off, and curls up beside you, remember that they’re not just bringing companionship into your home. They may also be bringing a little bit of the outside world with them.
Source: “Our Best Friends: How Dogs Alter Indoor Air Quality,” published in Environmental Science & Technology (2026).
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