Dogs and humans share a long history. Indeed, it is claimed that dogs are the first domesticated animal. (1) While canine companionship is believed to actively support mental well-being, (2) its impact on human physical health remains unclear. Some studies suggest that having a dog in the household enhances physiological health, especially in children, where early exposure to associated microbes may lead to lower asthma risk and respiratory tract illness. (3−7) Despite the mixed evidence regarding a protective effect of dog ownership against asthma and allergies, (8) elevated risk is typically observed only among sensitized individuals. Understanding these health effects requires a dedicated examination of the pollutants that dogs emit and their impact on indoor exposures─an area that remains largely unexplored.As mammalian vertebrates, dogs and humans share certain physiological processes, which may result in similarities in pollutant emissions. Earlier research has established humans as prodigious sources of indoor gaseous and particulate pollutants, as well as of microbes. Some of these emissions arise from endogenous processes: for instance, humans release carbon dioxide (CO2) and a suite of volatile organic compounds (VOCs) through respiration, (9−11) and ammonia (NH3) through the skin. (12,13) Additionally, skin shedding contributes significantly to indoor particulates and microbial matter. (14−16) Other emissions are exogenous; for example, interactions between ozone and skin oils produce various VOCs and ultrafine particles. (17−20) Human skin and clothing also serve as carriers, transporting gases, particles and microbes between environments. (21,22)

Building on our understanding of human emissions, we hypothesize that dogs may exhibit similar emission behaviors. However, the physiological differences between dogs and humans─such as variations in hair coverage, skin lipids, and sweat glands─are likely to result in distinct emission profiles. Surprisingly, despite the ubiquity of dogs in homes worldwide and their frequent physical interaction with humans and surfaces, no prior studies have systematically quantified the chemical, particulate, and microbial emissions from dogs. While dogs are known to affect indoor microbial environment, a simultaneous and controlled quantification of their chemical, particulate and microbial emissions is lacking. This represents a critical gap in our understanding of indoor air quality and exposure.

To address this gap, we conducted a pioneering experimental study to quantify the gas-phase and particulate emissions from dogs under controlled conditions. Using a state-of-the-art climate chamber, we measured a comprehensive suite of pollutants, including CO2, NH3, VOCs, 1–3 nm nanocluster aerosols, 1–10 μm total and fluorescent particles, as well as bacterial and fungal microbiota. Emissions from groups of big and small dogs were contrasted, and then compared to those from humans. The findings establish a foundation for a comprehensive understanding of the role of dogs in shaping indoor air quality and their potential contribution to human health through this pathway...