Avoiding Cats, Dust Doesn't Prevent Asthma

Early-Life Exposure to Allergy Triggers Decreases Allergies, Asthma, Study Shows

From the WebMD Archives

Sept. 29, 2004 -- Allergies are often closely linked to asthma, a condition that has been rapidly rising in recent years. But a new study shows that taking steps to rid your home of allergy triggers does little to help prevent asthma.

A new study from the National Heart and Lung Institute of the U.K. shows that reduced exposure to household allergy triggers like cat dander and dust mites does not protect against the development of childhood asthma and respiratory allergies. Kids exposed to more allergens actually had a lower incidence of these conditions.

The findings question the widely accepted notion that minimizing early-life exposure to dust, dirt, and dander protects children against asthma and allergies.

"In practical terms, what this means is that efforts to reduce allergens in the home are not likely to be a good way of preventing asthma," lead researcher Paul Cullinan, MD, tells WebMD. "We didn't look at whether keeping your house as free of allergens as possible helps in the treatment of kids who already have these conditions, but from a prevention point of view this is a dead issue."

Cats and Mites

Cullinan and colleagues followed 550 children from birth in southern England. The study appears in the October issue of the journal Thorax.

Household exposures to dust mites and cat dander were tested when the children were just over 2 months old. Their mothers were asked to report any wheezing, a symptom of possible asthma. When the children reached age 5 1/2, they were tested for allergies to dust mites, cat fur, and grass pollens.

Overall, 10% of the kids were allergic to dust mites or cats at age 5 1/2 -- in line with allergy rates from the general population. About 7% had episodes of wheezing.

But kids who were exposed to low levels of allergy triggers were at highest risk of developing allergies and asthma. Kids exposed to higher levels of allergens were less likely to develop these conditions.

The newly published study at least partly contradicts the findings of a similar German study -- one of the only other trials to look at this issue and follow children from birth. That study found a strong relationship between exposure to dust and dander and development of allergies and asthma. But most of the children had a high risk for these respiratory conditions -- likely due to having other family members with these conditions. This was not the case with the current U.K. study.

In an editorial accompanying the study, asthma expert Adnan Custovic writes that the seemingly contradictory findings imply that a one-size-fits-all approach to prevention may not be the best strategy.

Down on the Farm

The U.K. study is not the first to find that early exposure to allergens may actually protect children against developing asthma and allergies. Several recent trials have found a very high level of protection among children who grow up on farms, where exposure to certain allergens is very high. In one such study from Australia, exposure to horses and stables before the age of 1 was found to be highly protective against asthma and hay fever.

Researchers are just beginning to study the implications of these findings in terms of preventing these respiratory conditions.

"It may be that this research leads to some kind of vaccine or immune therapy, but at best that is years away," Cullinan says. "Right now all we know is that there is something about living on a farm that is very, very protective."

Show Sources

SOURCES: Cullinan, P. Thorax, October 2004; online edition. Paul Cullinan, MD, department of occupational and environmental medicine, Imperial College School of Medicine, National Heart and Lung Institute, London. Adnan Custovic, professor, North West Lung Centre, Wythenshawe Hospital, Manchester, England.
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