The Protective Effect of Cats

March 12, 2001 -- If you're a parent worried about your child getting asthma -- don't throw the kitty out with the litter! New research shows that having a cat in the house may actually keep certain youngsters from developing the debilitating illness.

"We've shown that many children who live with a cat do not become allergic despite very high exposure to cat allergen," says lead researcher Thomas Platts-Mills, MD, PhD, head of the Asthma and Allergic Disease Center at University of Virginia Health System in Charlottesville. Instead, he says, they exhibit a "modified response" to the allergen.

This modified response has all the characteristics of a normal allergic response, explains Platts-Mills, except the children do not produce any immunoglobin E -- the antibody that causes sneezing, wheezing, and makes allergy tests come out positive.

So while the kids are still having an antibody response, it's of a sort that does not lead to allergy symptoms. As a result, he tells WebMD, these children are 'tolerant' of cat dander and also do not develop asthma from this source.

The researchers tested the blood of more than 200 seventh and eighth graders, about 50 of whom had asthma, looking for antibodies. They exposed the children to dust mite and cat allergen.

Exposure to increasing levels of dust mite allergen always caused antibodies and symptoms to increase, but though increasing levels of cat allergen also caused antibodies to increase, it decreased symptoms. And those children who reacted and had symptoms -- who were 'sensitized' -- to either dust mites or cats were most likely to have asthma.

The findings are published in the March 10 issue of The Lancet.

"At lower levels, cat allergen may sensitize children and be a risk factor for asthma, but children exposed at higher levels may be protected because of a sort of desensitization process," says Bruce Lanphear, MD, associate professor of pediatrics at Children's Hospital Medical Center in Cincinnati, Ohio. "So cat allergen may be a cause of [allergy and asthma], but at the same time heavy doses may desensitize children so they don't get asthma." Lanphear reviewed the paper for WebMD.

The findings punch holes in several theories about why more and more kids seem to be developing allergies and asthma, says Platts-Mills. In northern Sweden, where children with pet cats show the same protection from asthma, the climate is far too cold to harbor dust mites. Yet, asthma continues to increase. So the rising asthma rate can't simply be due to increased allergens in the environment.

Nor can it be due to the so-called 'cleanliness hypothesis' that says that too little 'dirt' -- allergens or germs -- can leave our immune systems weak and unable to fight off whatever comes our way.

"This study is evidence against this simplistic theory that immunizing kids and keeping them away from allergens increases asthma," says Alan Harsch, MD, an associate professor of pediatrics in the pediatric pulmonology division at Emory University School of Medicine. He also reviewed the work for WebMD.

So what is to blame for this apparent surge in asthma? According to Platts-Mills, it's "the decline in exercise." He tells WebMD that "physical activity is the best protection against wheezing, and the lack of physical activity [in today's children] is responsible for the increase in symptoms."

The study only begins to explain what might be going on, the experts agree. Nonetheless, parents should feel comfortable that "having a cat in the house does not increase the risk that a child will become allergic in the first place," so there's no reason to get rid of your pet, says Platts-Mills. However, if a child does happen to become allergic, parents should remove the cat. "Once you become allergic, you are at increased risk of developing asthma," he says.

On the other hand, you "can't tell people to get a cat and it will make their children less likely to get asthma," warns Harsch. Children will react differently, and at least for now, there is no way to predict their individual response.

"Some children will have no response and no antibodies at all, even if they've lived with a cat all their lives. Other children become allergic. But then there is this interesting third group who become actively tolerant, who have this modified response, " Platts-Mills tells WebMD. At this time, there is no way to know which child will fall into which group.