(Reuters Health) – For children at higher than-average risk of asthma, having a dog around the house may increase the chances of developing the lung disease, a new study suggests. The study, which followed 380 children at increased risk of asthma due to family history, found that those exposed to relatively high levels of dog allergen at the age of 7 were more likely to have asthma. In contrast, there was no relationship between cat-allergen exposure and a child’s risk of asthma, according to findings published in the journal Pediatric Allergy and Immunology. Exactly why dogs were related to a higher risk of asthma, while cats were not, is not entirely clear. But one factor may be endotoxin, a substance produced by bacteria that is known to trigger inflammation in the airways, explained lead researcher Dr. Chris Carlsten, of Vancouver General Hospital in BC. “Dogs tend to have a lot of endotoxin on them, because they’re dogs,” Carlsten told Reuters Health. In contrast, cats have much less, he said.