May 23, 2001 -- Even if cats and dogs make you sneeze, will you save your kids from aggravating allergies by getting them a pet? It's a theory -- sometimes called the "hygiene hypothesis" -- that's been tossed around for a few years now, and evidence is mounting that it may be true.
In fact, a new study found that exposure to pets in a child's early years might "significantly lower risk," writes researcher David R. Ownby, MD, a pediatric allergy specialist at Medical College of Georgia, in Augusta. Ownby, and colleagues from the Henry Ford Health System in Detroit presented their study findings at this week's International Conference of the American Thoracic Society held in San Francisco.
The researchers followed a group of about 500 children, almost equally split among boys and girls, from birth to age 7. Children were checked regularly with blood tests to measure antibodies that cause allergies; skin reaction tests that show sensitivity to an allergen; and a pulmonary test to measure lung function, to detect asthma.
Researchers also collected data on exposure to cigarette smoke, home and day care environments, and measured allergen levels in household dust and air samples. They also asked about pets kept in the homes.
They found that children who lived with two or more animals were significantly less likely to have a positive skin test, signifying a reaction to an allergen, than those who had no exposure to pets. Children with pets were also less likely to have allergen antibodies.
Boys especially seemed to benefit from pet exposure. Not only did they have lower antibody levels, they had better lung function and therefore less evidence of asthma.
"We conclude that exposure to two or more cats and dogs reduces a child's risk of [allergies] and leads to better lung function in boys," write the authors.
"Ownby is a well-known allergy researcher, very well respected," says David Rosenstreich, MD, director of allergy and immunology at Albert Einstein School of Medicine in New York.
The study "adds to the growing support for the hygiene hypothesis, that the cleaner we live -- our western world lifestyle -- the more likely we'll get asthma and allergies," he tells WebMD. "It confirms that observation, that children with a history of pet exposure in the first years of life have less asthma."
Boys do tend to get more asthma and allergies, says Rosenstreich. "So it's not surprising [Ownby] saw greater reductions in the boys."
However, the study falls short of proving that pets can prevent allergies and asthma. "You shouldn't automatically get two cats and dogs," he tells WebMD. "It may be true, but that hasn't been proven in this study." Only a randomized study -- one in which families are assigned to keep pets or not keep pets in the house -- would truly prove the hypothesis.
It could be that Ownby's study shows only that children who have a risk of allergy or asthma tend not to keep cats and dogs in the house, Rosenstreich says.
Working on the same 'hygiene hypothesis,' pets might not even be a necessary factor in increasing a child's immunity, says David Skoner, MD, director of allergy and immunology at Children's Hospital in Pittsburgh.
Siblings might also fill the bill, Skoner tells WebMD. "Early life infections may help drive the immune system away from allergy ... [and] kids can get this kind of exposure from older siblings in the first six months of life -- or from day care. That might ultimately reduce risk of allergy. But then again, nobody's saying yet put them in day care."
"Evidence is mounting [for the hygiene hypothesis]," says Skoner. But more studies like Ownby's need to be done, following children during their early lives.