Oct. 14, 2003 -- Despite the long-held belief that cats and dogs in the home could lead to childhood allergies, there's mounting evidence that the opposite may be true: Having pets may actually reduce risk while avoiding these critters doesn't.
In the latest study, allergist Thomas Platts-Mills, MD, PhD, of the University of Virginia, and Swedish researchers find that the longer children had pets when they are young -- ideally during their first two years -- the lower their frequency of having pet allergies is years later.
It follows a study last year that found babies raised in a home with two or more dogs or cats were up to 77% less likely to develop various types of allergies at age 6 than kids raised without pets. Besides pet allergies, those children were less likely to develop reactions to dust mites, ragweed, and grass.
Both findings go against the long-held belief that exposure to pets in childhood could increase risk of developing allergies.
The new study, published in this month's issue of The Journal of Allergy and Clinical Immunology, is based nearly 2,500 children in Sweden. They were tested for allergies between ages 7 and 8 and again four years later.
Children who continually owned pets were less likely to have pet dander allergies than new pet owners or those who had only been exposed earlier in life. In fact, of those who proved to be allergic to cats, 80% never had a cat at home.
Platts-Mills tells WebMD that in his study, the protective effect of pet ownership was much stronger with cats than with dogs.
"Based on these findings, we can certainly say that if you are considering getting rid of the animal because you want to have children and are worried about their allergies, there is no reason to do that," Platts-Mills says.
This is significant, because allergies often run in families and children of parents who are allergic -- whether to pet dander or other allergens -- are more likely to develop their own allergies.
Still, he's not ready to suggest that you get a pet if you don't already have one. Platts-Mills notes that his study was done in Sweden, where dust mite allergies are less common than in the U.S. Since pets produce more dust, having dogs and cats can aggravate dust mite allergies in people vulnerable to them.
"We still do need to identify people who would especially benefit from having a pet," he says. "But because of this and other studies, we now believe that while pet dander is a potent allergen in some children, it may also produce a tolerance in others. Having a pet goes both ways."
Allergist Dennis Ownby, MD, of the Medical College of Georgia, researcher of last year's study, says he isn't surprised by Platts-Mills' new finding.
"There are now probably a half-dozen prospective studies that are fairly consistent in finding that early pet exposure reduces allergy risk," he tells WebMD. "What is surprising is in the number of details: Some people say that children of allergic parents have no effect by being exposed to a dog or cat, but others, like our study, see a larger protective effect when parents do have allergies.
"The theory that Dr. Platts-Mills is proposing is that very low levels of pet allergen exposure don't do anything. As you get slightly higher, you increase the risk that you become allergic to the pet. But quite high pet allergen exposure may lead to changes in the immune system so that it is less likely to produce an allergic response."