TUESDAY, Aug. 27, 2002 (HealthDayNews) -- Pets have long been blamed as a major source of allergens in the home, but a new study may give them at least a partial furlough from the doghouse.
Researchers say some children exposed as infants to two or more pets in the house are less -- not more -- likely to develop allergies to dogs, cats, and other irritants later.
The findings, appearing in tomorrow's issue of the Journal of the American Medical Association, confirm earlier, counterintuitive studies from the United States and abroad showing that pet dander seems to protect children from allergies and asthma.
"For years, I've been telling people concerned about their kids and allergies that they ought to get pets out of the house," said Dr. Dennis Ownby, an allergist at the Medical College of Georgia and leader of the research team. "Now I have to retract that and tell them, 'If you're happy with pets in the home, you can continue to have them without feeling guilty.'"
Ownby took the matter a step further. "If you're going to have a pet," he said, "it's probably better to have two rather than one."
Ownby said there's a debate about why early exposure to pets is protective. His group's feeling is that animals may track in irritants from the dirty world outside the home that beef up a child's immune system. The generally increasing cleanliness in developed countries has been blamed for a recent surge in allergies and asthma.
"This suggests that there is something we can do that will, in fact, reduce risk, and if we could define what it is, maybe we could refine that and give it to kids" as a way to shield them from allergies, Ownby said.
Scientists long believed that pets posed a major source of household allergens -- and for some people that's certainly true, said Dr. Thomas Platts-Mills, an allergy expert at the University of Virginia in Charlottesville.
But, he said, there are children "who would be allergic otherwise, but because there's a cat in the house, they don't become allergic to the cat. That's very, very important, because it implies that high-dose natural exposure can give rise to a form of tolerance."
Platts-Mills, author of an editorial accompanying the journal article, estimated that as many as 20 percent of people may develop tolerance to pet allergens by living with animals.
"That's a big phenomenon," he said.
Platts-Mills, who published a study last year showing that exposure to cats can be protective against allergies, added that researchers have come to realize that not all irritants are created equal -- a commonly held view until only lately. "Twenty years ago we were really thinking it's all the same thing," he said.
In the latest study, Ownby and his colleagues followed 474 Detroit-area children from birth to age 6 or 7. By then, 33.6 percent of those with no cat or dog at home during their first year of life had developed skin sensitivity to six common irritants, including dust mites and pollen. That figure was slightly higher for those with one cat or dog, but it plunged to 15 percent among the 78 children with at least two pets.
The protective effect of having at least two animals at home during infancy was equally impressive on the number of children with blood markers for sensitivity to any of seven allergens.
After adjusting for factors that exacerbate allergies, including exposure to cigarette smoke, dust mites and a parental history of asthma, having two or more cats or dogs in the house while the child was an infant reduced the kid's risk of allergies by between 67 and 77 percent, compared with having one pet or no pets.
"This apparent protective effect includes all allergens, at least the ones we tested, and not just the one [the children] were exposed to," Ownby said.
Intriguingly, and for reasons the researchers don't understand, boys appeared to gain more lung protection from pets than girls did.
Yet even if pets may provide protection against allergies, some allergists aren't advising parents to try a little fur therapy for their children.
"Ten percent of children are allergic to cats and they're at risk of asthma, so telling people to get a cat might help some and harm others," Platts-Mills said.
Dr. Clifford Bassett, an allergy expert at the New York University School of Medicine in Manhattan, agreed.
What's more, he said, the findings don't apply for those who already react badly to animals.
"People who have pet allergies that have been diagnosed should continue to avoid pet exposure," Bassett said.
What To Do
For more on allergies, try the American Academy of Allergy, Asthma and Immunology. And for a look at how allergens trigger an immune reaction, check out HowStuffWorks.
