Infants who live in homes with two or more cats or dogs appeared to be at less risk for developing allergic reactions that lead to asthma, a new study has found.

The 10-year study showed children who were exposed to the furry pets during their first year of life were half as likely to develop common allergies by about age six than those living in petless homes.

Researchers at the Henry Ford Hospital in Detroit tracked 474 healthy, mainly Caucasian infants from birth to age six. Their study appears in the Aug. 28 issue of the Journal of the American Medical Association.

Thumbs, er, paws up for infants playing with dogs

They found about one-third of the kids who lived in homes without animals, or with one cat or one dog, tested positive for allergic sensitivities in skin prick tests to several common allergens, such as dust mites, dog, cat and ragweed by age six.

Only 15 per cent of children in homes with two or more pets tested positive for allergy, the study said.

Researchers took into account parental smoking, dust mite levels, older siblings and the presence of Fido and Fluffy later in childhood. But the study included only 78 kids with two or more animals, which makes it difficult to generalize the findings, the authors said.

Cats get OK, too

Pets welcome

Previous studies concluded early exposure to dogs and cats increased the risk of asthma in children older than six. Traditionally, allergists have recommended parents with a history of allergy reduce the risk for their children by not keeping pets.

Epidemiologist Christine Cole Johnson of Henry Ford Hospital was one of the study's investigators.

"While more research is needed, if an expectant parent with a history of allergies came up to me and wondered whether the cats or dogs had to go, I would tell them to keep the pets," Johnson said.

The study's authors said more research is needed to determine if the effect lasts beyond age six or seven, and to explain the underlying reasons for the conflicting findings.

Immunologist Dr. Peter Vadas directs the division of allergy and clinical immunology at St. Michael's Hospital in Toronto. Vadas, who wasn't involved in the study, said the potentially protective benefits of early exposure to pets are well documented.

Johnson said researchers theorize that exposure to cats and dogs may influence the development of a child's immune system. Pets are associated with bacterial endotoxins, which are thought to cause the immune system to respond differently and protect against allergies.

Early exposure to pets could also cause the immune system to produce protective antibodies without allergic sensitization, the authors said.

The research was funded by the National Institute of Allergic and Infectious Diseases, Henry Ford Hospital and by a grant from the National Institute for Environmental Health Sciences.