Mom's the Key to Cats Curbing Asthma in Kids

New research adds a caveat: If mother has history of wheezing, kid's risk is also high

THURSDAY, Sept. 5, 2002 (HealthDayNews) -- Babies exposed to a cat at home gain protection from later allergies -- unless their mother has a history of asthma.

That's the conclusion of a new study that adds to the growing body of evidence suggesting that pets often prevent rather than aggravate childhood allergies.

"Even in this high-risk group, exposure to a cat in early childhood was protective against wheezing in the first five years of life," said Dr. Juan Celedón, a researcher at Brigham and Women's Hospital in Boston and lead author of the study. "It could be that exposure to these pet allergens influences the immune system of newborns so that it goes into a non-allergic mode."

However, Celedón said the new study does sound a note of caution for some children: Those whose mothers had a history of asthma were more prone to wheezing at age 3 or later if exposed to a cat as infants. The reason could be genetic or perhaps some shared environmental influence either during pregnancy or shortly after birth, Celedón said. The study couldn't say. Nor, Celedón added, did the researchers look at whether the children of women allergic to cats were more likely to be allergic to felines themselves.

Whatever the case, dogs appear to be off the hook: Celedón's group found no link between exposures to dogs and their allergens and childhood airway troubles. A report on the findings appears in the Sept. 7 issue of The Lancet.

The study followed 448 children from birth to age 5. All had at least one parent with a history of allergies or asthma -- known collectively as atopy -- putting them at increased risk of the conditions. The researchers periodically interviewed parents about their child's lung health. They also collected household samples to determine levels of pet allergens.

Celedón's group found no connection between early exposure to a cat and future chronic wheezing in kids whose fathers had atopy. But those whose mothers were asthma-free had a 40 percent lower risk of wheezing if a cat was around during their first two months of life than those not exposed to the animals. That was true even if the mothers had allergies.

These children also had lower blood levels of an immune protein called IgE, which is an indirect marker of sensitivity to irritants. This molecule predicts risk of allergies, though not their severity.

Those whose mothers had asthma, on the other hand, were three times as likely to develop airway distress by the time they were 5 if exposed to a cat during infancy. They seemed to "become sensitized to cat allergen in early life and wheeze afterwards when re-exposed," the study said.

"It's a very interesting story that's emerging here," said Dr. Gerald Gleich, a dermatologist at the University of Utah, referring to the string of studies, including the latest one, showing a protective benefit from household pets.

Gleich counts himself in the camp of experts who believe in the "hygiene hypothesis" -- which states that as the developed world becomes cleaner, children are exposed to fewer irritants as their immune system matures.

"Our environment is actually quite clean now, so clean that the filth and feces that had been our lot in the past has been significantly cleaned up. The immune system doesn't see all of the signals that it had seen in years gone by," he says.

The result is an epidemic of allergies and asthma -- except, perhaps, in the children who are primed early on by irritants like those shed by household pets.

But while Gleich believes the latest findings bolster the hygiene hypothesis, they do so with a twist. "There's a maternal influence that overrides the [cat allergen] exposure effect," he said. "What that is is obscure."

What To Do

For more on allergies, try the American Academy of Allergy, Asthma and Immunology. And for a look at how allergens trigger an immune reaction, check out HowStuffWorks.

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