The Californian researchers looked at the relationship between chronic cough, phlegm production or bronchitis and dog and cat ownership among 475 southern California children with asthma who participated in the Children's Health Study, a longitudinal study of air pollution and respiratory health. Children with dogs had significantly increased cough, phlegm production and bronchitis responses to the measured pollutants, including nitrogen dioxide, ozone, particulate matter and acid vapour. There were no increases of these symptoms in children who lived in homes without pets or who lived with only cats.

"Further work is needed to determine what it is about dogs that may increase an asthmatic child's response to air pollution," says Rob McConnell, M.D., professor of preventive medicine at the Keck School of Medicine of USC and lead author of the study. McConnell and colleagues speculated that the increased response to air pollution from a dog in the home may really be due to increased levels of endotoxin, which is more common in homes where there is a dog.

"Cats are highly allergenic, and children with asthma are often allergic to cats," says McConnell. "Therefore if an allergen were enhancing the lung's response to air pollution, we'd be more likely to see an association with cats. But in this study we see an effect of air pollution in homes with dogs, so we think endotoxin exposure is a more likely explanation for our results than allergen exposure."

"There's experimental literature that shows both allergens and endotoxin interact with air pollution and increase the effect of each other," explains McConnell. "But there's been very little study to see if these experiments have relevance for the general population of children with asthma."; Source: University of Southern California