People with asthma may be putting their health at risk by keeping a dog, scientists have warned.
More than a third of asthmatics were allergic to dogs
The family dog is more likely to cause health problems for asthmatics than a cat, according to a study.
It has long been known that allergies to pets can trigger asthma.
The cat has always been thought to be the worst offender but now the dog is firmly in the frame.
US experts looked at the effect of allergens from pets, insects and plants on asthma sufferers. The results were surprising.
"Although a greater number of people had reactions to cat allergen, dogs came out on top as promoting greater disturbances in pulmonary function measurements for asthmatics," said lead author Tim Craig, professor of medicine and paediatrics at Penn State College of Medicine.
"This may be surprising to many because it dispels the myth that cats cause more severe allergic reactions."
The team looked at how 809 adults with asthma reacted to allergens from animals and plants, including dogs, cats, cockroaches, mould, mites, grasses, trees and weeds.
They assessed the patients' sensitivity to each allergen using skin tests and three measures of lung function.
They found that cats were most likely to provoke a reaction - 72% of patients were allergic to them.
This is an interesting study which demonstrates the complex relationship between how allergens affect people with asthma.
Far fewer patients - 38% - were allergic to dogs, but they were the only animals to affect all three lung function tests.
This suggests dog allergens are more of an irritant than cat allergens.
"This study shows that we, as clinicians, should be as diligent as we can in convincing people that they should consider their pets as a possible factor when trying to control their asthma," said Prof Craig.
UK charity, the National Asthma Campaign, believes more research is needed to understand why.
"In this American study, whilst a higher percentage of people are affected by cat allergens, dog allergens were shown to cause worse symptoms," said a spokesperson.
"This is an interesting study which demonstrates the complex relationship between how allergens affect people with asthma."
The results were presented at the American Thoracic Society International Conference in Seattle.