Cockroaches worsen asthma symptoms in children far more than furry pets or dust mites, U.S. researchers reported on Tuesday.

High-rise apartments in Northeastern U.S. cities were the worst places for the allergic effects of cockroaches, the team at the University of Texas Southwestern Medical Center in Dallas found. Single-family houses were the worst for dust mites - microscopic creatures that live in bedding and furniture.

“We found that a majority of homes in Chicago, New York City and the Bronx had cockroach allergen levels high enough to trigger asthma symptoms, while a majority of homes in Dallas and Seattle had dust mite allergen levels above the asthma symptom threshold,” said Dr. Rebecca Gruchalla, who led the study.

“These data confirm that cockroach allergen is the primary contributor to childhood asthma in inner-city home environments,” added Kenneth Olden, director of the National Institute of Environmental Health Sciences, which helped fund the study.

“However, general cleaning practices, proven extermination techniques and consistent maintenance methods can bring these allergen levels under control.”

Cockroaches produce allergic reactions from their saliva, fecal material, secretions and cast off skin.

“Children who tested positive for, and were exposed to, cockroach allergen experienced a significant increase in the number of days with cough, wheezing and chest tightness, number of nights with interrupted sleep, number of missed school days, and number of times they had to slow down or discontinue their play activity,” Gruchalla said in a statement.

Writing in the March issue of the Journal of Allergy and Clinical Immunology, Gruchalla and colleagues said they tested 937 inner-city children aged 5 to 11 with moderate to severe asthma symptoms.

They were tested for sensitivity to cockroach and dust mite allergens, pet dander and mold. Bedroom dust samples were analyzed.

This study was part of the larger Inner-City Asthma Study, which includes seven asthma centers across the United States.