"[The] dust mite is clearly, any way you cut it, important, and so is environmental tobacco smoke, and then cats and cockroaches in terms of flaring up asthma ... those are bad actors," Richard Johnston Jr., MD, tells WebMD. Johnston headed the committee that produced the analysis called "Clearing the Air: Asthma and Indoor Air Exposures" for the Institute of Medicine (IOM). The IOM is an independent advisory group chartered by the National Academy of Sciences.
The IOM document hopes, in part, to address the increasing problem of asthma in the U.S. -- particularly among inner-city blacks.
While asthma appears to be caused by a mix of genetic and environmental factors, the condition, which afflicts some 17 million Americans, is still poorly understood, according to Johnston. "The document serves as a guide, basically. It's a strategic plan and statement of where the needs are," says Johnston, a professor of pediatrics at the University of Colorado School of Medicine.
In its review, the IOM committee surveyed a wide variety of studies linking asthma and indoor air. Among the issues studied were animal, plant, and chemical allergens and irritants, as well as dust mites, cockroaches, fungi and mold, dander, hair and saliva from domestic pets, and a number of other factors.
The results were then divided into agents that could cause or lead to the development of asthma and things that could make the condition worse. Only the dust mite gathered enough evidence to rank as an asthma cause. However, environmental tobacco smoke in young children was strongly associated with the breath-stealing disease. There was limited data on the relationship between cockroaches and asthma in infants, says the IOM committee, and there wasn't enough information to show if cats, dogs, or fungi and molds were asthma causes.