Dog and cat lovers can put aside their differences and celebrate a common cause. Researchers have demonstrated that exposure to two or more dogs or cats in the first year of a child's life reduces the risk of developing allergies later on.
More than 20% of the U.S. population suffers from the wheezy, itchy, watery-eyed misery of allergies. Reactions can be triggered by just about anything, but the most common culprits include dust, pollen, and pet dander. Doctors diagnose allergies by injecting tiny amounts of allergens and then waiting to see whether hives develop, or by analyzing blood serum for allergen-specific antibodies.
Pediatric allergist Dennis Ownby of the Medical College of Georgia in Augusta and his colleagues studied 474 children from birth until their sixth birthday to determine whether pet exposure impacts the risk of allergies. They annually recorded the number of cats and dogs in the child's home, along with other variables such as exposure to cigarette smoke, dust levels in the child's bedroom, and whether parents suffered allergies. When the youngsters turned 6, researchers collected blood samples and conducted skin prick tests for dog, cat, and common allergens such as dust mites and ragweed pollen.
The tests showed that--after controlling for other, potentially confounding variables--only 18% of children exposed to two or more pets in the first year of life had any allergies, compared with 39% in the group with no pets at all. And surprisingly, exposure to several pets not only created a tolerance to pet dander, but to other common allergens as well, the team reports in the 28 August Journal of the American Medical Association. These findings fly in the face of the commonly held idea that early exposure to allergens increases the risk of allergies.
The overall reduction of sensitivity was unexpected, says allergist David Golden of Johns Hopkins University in Baltimore, Maryland. "Immunologists are going to be struggling to explain this," he says. Apparently, heavy exposure to allergens within the first year helps to desensitize the immune system, he says.