MONDAY, June 13 (HealthDay News) -- Exposure to pets in infancy and childhood probably won't increase a child's risk of developing an allergy to cats and dogs, and may actually protect against such allergies, new research suggests.
The first year of life appears to offer the greatest protection, the researchers said. Living with a dog before age 1 year was associated with about half the risk of developing a dog allergy in boys. Exposure to cats before turning 1 was associated with about a 48 percent reduction in risk for girls and boys, the new study reported.
"Exposing children to cats and dogs in the home is not going to increase the risk of sensitization to these animals. It might even decrease the risk," said the study's lead author, Ganesa Wegienka, an epidemiologist in the department of public health at Henry Ford Hospital in Detroit.
Results of the study are published online June 13 in the journal Clinical & Experimental Allergy.
As many as 70 percent of U.S. households have pets, according to estimates from the American Academy of Allergy, Asthma and Immunology. For those who are allergic to these animals, symptoms can range from watery eyes, a runny nose and sneezing to a full-blown asthma attack.
But experts haven't been sure if early exposure to animals might contribute to the development of those allergies. Some experts think that early exposure could trigger the development of allergies, while others suspect that early exposure could increase the immune system's exposure to a diverse array of bacteria, making it less likely to overreact to normally harmless substances, such as animal dander. This theory is commonly referred to as the hygiene hypothesis.
To see what effect, if any, childhood exposure to cats and dogs has on the development of pet allergies in children, the researchers tested blood samples gathered as part of the Detroit Childhood Allergy Study for the presence of a substance known as animal-specific IgE. The presence of this antibody would indicate that an individual was "sensitized" to that animal, which indicates an allergy. The study began in 1987.
At age 18, about 560 of the study's participants agreed to participate in this follow-up study. They provided additional blood samples and pet histories.
During their first year of life, 184 teens had an indoor dog and 110 had an indoor cat.
In males, the risk of having a dog allergy was decreased by 50 percent in those who had a dog during their first year. This association wasn't found in females, however. But when the researchers looked at teens born via cesarean-section delivery, they found that both males and females had a 67 percent decreased risk of dog allergy when they lived with a dog during their first year of life.
Wegienka noted that babies born via C-section aren't exposed to the diverse microflora that babies born vaginally are, which might make their immune systems more susceptible to allergies.
The researchers said that exposure to animals at other times in childhood didn't appear to be as significant as the first year. But, Wegienka cautioned that this study doesn't prove a cause-and-effect relationship between having a pet and avoiding allergies, just an association between those two factors.
"We don't want to say that everyone should go out and get a dog or cat to prevent allergies," she said, adding that the current study only found an association between a reduced risk and exposure to cats and dogs. "More research is needed, though we think this is a worthwhile avenue to pursue. How does having a dog or a cat change the home environment? And, how does that affect allergy risk?"
The authors said it would be logical to look at smaller and smaller windows of time, such as the first month or first three months of life.
Dr. Jennifer Appleyard, chief of allergy and immunology at St. John Hospital and Medical Center in Detroit, said the development of allergies is very complicated. It's significant that this study found that early life exposure wasn't associated with an increased risk, she said.
"We're not likely to find one simple answer to avoid them [allergies], but this study suggests that maybe having pets -- whether or not it's protective -- maybe having them isn't so bad," Appleyard said.
For more on pet allergies, visit the American Academy of Allergy, Asthma & Immunology.
SOURCES: Ganesa Wegienka, Ph.D., epidemiologist, department of public health, Henry Ford Hospital, Detroit; Jennifer Appleyard, M.D., chief, allergy and immunology, St. John Hospital and Medical Center, Detroit; July 2011, Clinical & Experimental Allergy
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