Asthma Triggers

by Laurie Barclay, MD
August 24, 2004

Medscape Medical News — Many asthmatics are sensitive to airborne molds rather than to pollens or animal dander, according to an epidemiological survey published in the Aug. 24 issue of the British Medical Journal.
"Sensitization to molds is a powerful risk factor for severe asthma in adults," write Mahmoud Zureik, from the National Institute of Health and Medicine Research (INSERM) in Paris, France, and colleagues. "This should be taken into account in primary prevention, management, and patients' education."

Investigators in this cross-sectional study from the European Community respiratory health survey analyzed data from 1,132 people with asthma, aged 20-44 years. The frequency of sensitization to airborne molds increased significantly with increasing asthma severity (odds ratio 2.34, 95% confidence interval 1.56 to 3.52, for severe vs. mild asthma). There was no association between severity of asthma and sensitization to pollens or cats.

The authors suggest that fungi are more likely to exacerbate asthma than is pollen or animal dander because the small size of fungal spores may allow them to reach the lower airways; molds are present throughout the year; and most asthmatics spend more time indoors where molds are more prevalent.

"Those people with asthma who are sensitized to airborne molds should be educated to pay careful attention to symptoms and comply with treatment, particularly during the seasonal increase in mold spore counts," the authors write. "Patients should be encouraged to decrease exposure by avoiding indoor conditions that facilitate the growth of molds — for example, by better ventilation and by decreasing dampness."

Molds and Asthma

Sensitivity to airborne molds can increase the frequency and severity of asthma symptoms.

That's the claim of a European study in the British Medical Journal.

The study used data from 1,132 people with asthma from the European Community respiratory health survey. The researchers found a strong connection between a person's sensitization to molds and the severity of their asthma, but found no such connection with pollen or cats.

The researchers suggest the small size of fungal spores of airborne molds let the spores enter a person's lower airways. Also, while pollen is present only at certain times, molds are present throughout the year and their spore counts just increase during autumn.

Mold exposure levels are probably greater than those of pollen because mold exposure occurs indoors, where people spend most of their time.

The study authors say people with asthma who are sensitized to airborne molds must pay close attention to their asthma symptoms and adhere to their treatment programs, especially during the fall when mold spore counts increase.

Improving the ventilation and decreasing the dampness in your house can also help decrease your exposure to molds, the authors say.

(SOURCE: British Medical Journal, news release, Aug. 23, 2002)

The American Lung Association has more information about asthma.

A new report from the Institute of Medicine (IOM) of the National Academies finds strong, causal evidence linking common indoor substances to the triggering or worsening of asthma symptoms in susceptible people. It also finds that a variety of strategies, such as removing a pet, intensive cleaning, prohibiting smoking, and controlling indoor humidity, often helps to alleviate asthma symptoms.

After reviewing the latest scientific studies, the committee that wrote the report concluded that exposure to allergens produced by house dust mites — found in nearly every indoor environment - can lead to asthma in children who are predisposed to developing the disease. In addition, exposure to these allergens, as well as those produced by cats and cockroaches, can aggravate symptoms in some asthma sufferers. The condition of asthmatic preschoolers also can be worsened by contact with secondhand tobacco smoke.

"The prevalence of asthma continues to rise dramatically in this country", said committee chair Richard B. Johnston Jr., professor, department of pediatrics, University of Colorado School of Medicine, and National Jewish Medical and Research Center, Denver. "People spend most of their time inside, and it’s vital that we understand how the indoor environment may contribute to the disease. Fortunately there are actions people can take to limit their exposure and ease symptoms".

Scientists think that some people are genetically predisposed to develop the disease. Whether they do depends on a complex—and at present poorly understood—combination of factors that are partially inherited and partially environmental. For example, dust mites are present in most indoor environments, so their mere existence is not the sole factor that determines whether a person will develop asthma.

The committee evaluated a broad body of research on asthma and indoor air, including population studies, clinical research, and studies on air flow and humidity in buildings. It looked at a range of potential indoor animal, plant, and chemical allergens and irritants in two ways: the extent to which each could lead to the development of asthma—the point at which a person first displays symptoms—or could worsen the condition of people who already have the disease. The indoor agents included allergens from dust mites and cockroaches; mold; dander, hair, and saliva from domestic pets and other animals; viruses and bacteria; spores and materials from houseplants; and irritants from secondhand tobacco smoke, pesticides, cleaning and building materials, and other pollutants.

The committee found varying degrees of evidence for some of the allergens and irritants. For example, secondhand tobacco smoke was very strongly linked to worsening asthma symptoms in preschoolers, but the evidence was unclear in the case of older children.

Based on the strength of the evidence, findings were placed into the following categories:

Evidence in this category is strong enough to conclude that an allergen or irritant causes symptoms to develop in predisposed individuals or to worsen in known asthmatics. The committee determined that exposure to molds and material shed by dust mites could lead to the development of the disease in susceptible people. Exposures that could cause symptoms to worsen in individuals sensitive to particular allergens are those associated with molds, dust mites, animal dander, and cockroaches. Exposure to secondhand smoke can also cause a worsening of asthma symptoms.

Evidence in this category is sufficient to conclude there is an association, but it stops short of a higher standard of proof needed for causality. The committee found sufficient evidence of an association between the worsening of asthmatic symptoms and exposure to dogs and rhinoviruses—the group of viruses responsible for the common cold and other respiratory illnesses. In addition, using older or malfunctioning gas appliances in poorly ventilated kitchens can sometimes result in brief, high levels of nitrogen dioxide, which can lead to problems for asthmatics who also are exposed to other forms of indoor pollution. Sufficient evidence also exists that preschool children are at greater risk of developing asthma from exposure to secondhand tobacco smoke.

A classification of limited or suggestive evidence means that while at least one major, high-quality population study has found a link between the disease and exposure, the evidence is not yet conclusive enough to say definitively that chance or study bias did not influence the results, or that the studies have isolated all of the variables that could have affected the outcome.

For biologic or chemical contaminants that could worsen asthma symptoms, limited or suggestive evidence exists regarding exposure to material shed by domestic birds; certain types of pneumonia and respiratory syncytial virus (RSV); secondhand tobacco smoke in older children and adults; formaldehyde fumes from furniture and building materials; and fragrances in personal care and household products. The committee found limited evidence of an association between the development of asthma in infants and their exposure to RSV and material shed by cockroaches.

The scientific evidence in this category was insufficient to determine whether an association exits between non-occupational indoor exposure to a number of potential contaminants and the development or the worsening of asthma. These included pesticides and other exposures from houseplants, as well as domestic or wild rodents.

For this category, several adequate studies are mutually consistent in showing no association between the action or agent and the outcome. The committee found that rhinoviruses did not appear to be associated with the development of asthma in adults.

Researchers have wondered whether indoor air quality may play a role in the increasing rate of asthma nationwide. About 17.3 million Americans have this long-term respiratory disease. Since 1980, the prevalence of asthma and asthma-related hospitalizations and deaths has increased 75 percent. It is the most common chronic disease among children. Of particular concern are the high death rates among African Americans with asthma and in urban areas that have substantial poverty and minority populations. Moreover, the phenomenon is not limited to the United States. The prevalence of the respiratory disease in some countries—including Australia, New Zealand, Ireland, and the United Kingdom—exceeds that in the United States.

The U.S. Environmental Protection Agency asked the IOM to assess the scientific literature regarding asthma and indoor air quality in an effort to ensure that its public health strategies and outreach are based on sound science.

The committee found that the effectiveness of steps to control indoor allergens or pollutants that can cause or aggravate asthma varies widely. Some strategies include:

Although the strategy may be unpopular, the removal of a pet known to be the source of an allergen may ease symptoms in sensitized individuals. A thorough cleaning of the home—especially carpets, bedding, and upholstered furniture—is a sound approach to controlling exposures to pet dander, mite or cockroach material, mold, or other problematic biologic agents. In addition, the combination of cleaning and pest extermination applied consistently and conscientiously over time is a more effective long-term measure than either cleaning or extermination by itself.

A complete cessation of smoking in the home and other indoor environments appears to be the only reliable means of protecting young children from exposure to secondhand smoke. Where possible, removing the source also works well for a range of other problematic chemical exposures.

Because asthma is a complex illness, more needs to be learned about the many variables that determine its development and severity, the committee said. For example, more research is needed to better judge whether various environmental interventions are effective in improving the health of asthmatics. While some interventions work at an individual level, it is not known whether they will be effective at a community level. These programs may have to be adapted to the special circumstances of target populations, such as poor and inner-city residents. Individuals living in public or rental housing, for instance, may not have the resources or authority to make changes to their environments, such as replacing carpeting, removing excess moisture, or exterminating pests.

Of particular interest is determining how some people become sensitive to certain allergens and develop asthma, the report says. There also is a great need for studies that examine the role of prenatal exposures and whether the age of first exposure influences the development of sensitization. This would aid in the design of more effective interventions.

The committee also called for more interactions between researchers, clinicians, public health professionals, and those who are responsible for the design and function of indoor environments, such as engineers, architects, and materials manufacturers. Better research is needed on optimal levels of humidity and ventilation for healthier indoor air, for example.

In general, it is not possible to quantify the risk of developing asthma from exposure to contaminants in indoor air, the committee said. The relative risk of exposure depends on widely ranging variables, such as the type of indoor environments and characteristics of people exposed.

The study was funded by the U.S. Environmental Protection Agency. The Institute of Medicine is a private, nonprofit organization that provides health policy advice under a congressional charter granted to the National Academy of Sciences.

You may view Clearing the Air: Asthma and Indoor Air Exposures online for free or purchase a printed version from the National Academy Press; tel. (202) 334-3313 or 1-800-624-6242.