According to a new study published this week in the online edition of the Environmental Health Perspectives Journal, dogs and smog simply don't mix, especially in the case of individuals with asthma. Researchers at the Keck School of Medicine of the University of Southern California (USC) suggest in their study entitled 'Dog Ownership Enhances Symptomatic Responses to Air Pollution in Children with Asthma' that keeping a dog around the house worsens the effects of air pollutants on asthmatic children's symptoms.

Investigating how the combination of dogs and air pollution influence respiratory disorders, scientists found that these are risk factors which enhance chronic cough, phlegm production and bronchitis responses in asthma patients. The USC team also found that asthmatic children living without any pets or having only cats around the house do not present such high risk of having their symptoms worsen as compared to those living with both dogs and cats or with dogs only.

Researchers admit that asthmatic kids are often allergic to cats, therefore these animals can be allergenic triggers, but dogs affect differently the symptoms of asthma. Dogs increase levels of endotoxin when bred in homes. Endotoxin is a bacterial toxin derived from the outer cell wall of some very common environmental bacteria - the Gram-negative bacteria. Experts involved in the study suggest that when inhaled by asthmatics, the harmful toxin produces an inflammatory response in patients' lungs and leads to the constriction of their airways.


"Cats are highly allergenic, and children with asthma are often allergic to cats. 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," explained leader of the study Rob McConnell, M.D.

"There are other possible explanations for the findings and actual measurements of home allergen and endotoxin, in addition to air pollution, would be important to evaluate further our hypothesis. It could also be that something only indirectly related to dogs could explain these results, for example that kids with dogs exercise outside more so they have more exposure to air pollution," he added.