Environmental Triggers of Asthma: NIH Guidelines for Control

Successful long-term management of asthma requires identification and control of environmental factors that increase asthma symptoms and/or precipitate exacerbations. The Expert Panel of the National Asthma Education and Prevention Program issued guidelines for controlling environmental factors¹; highlights of these recommendations are presented here.

The Expert Panel reviewed various environmental factors that contribute to asthma severity and suggested measures to control exposure. Among the factors are inhalant allergens, occupational exposures, and irritants.

INHALANT ALLERGENS
Exposure of vulnerable patients to inhalant allergens increases airway inflammation, airway hyperresponsiveness, symptomatology, need for medication, and incidence of fatal reactions. Thus, all patients with asthma should be queried about exposures to these substances and evaluated for allergen sensitivity.

Diagnosis. Determining a patient’s relevant inhalant sensitivity will enable you to recommend specific environmental controls to reduce exposure. It will also help the patient understand the pathogenesis of asthma and the value of inhalant allergen avoidance. First, determine the patient’s exposure to allergens (Box). Then assess the patient’s sensitivity to these allergens:

• Use the medical history to determine sensitivity to seasonal allergens.
• Use skin testing or in vitro testing to determine the presence of specific IgE antibodies to perennial indoor allergens.
• Assess the clinical significance of positive allergy tests in the context of the patient’s medical history.

Management. The most important step in controlling allergen-induced asthma is to reduce exposure to the offending substances. These include indoor allergens—such as animal dander, house dust mites, cockroach allergens, and indoor fungi (molds)—and outdoor allergens, such as pollen (Figure). The Expert Panel emphasized that a multifaceted, comprehensive approach is required for effective allergen avoidance; individual steps alone are rarely sufficient.

Immunotherapy. Consider immunotherapy for asthmatic patients when there is clear evidence of a relationship between symptoms and unavoidable exposure to a relevant allergen; when symptoms occur either all year or during a major portion of the year; and when pharmacologic management of symptoms is difficult. Although several studies of immunotherapy with certain single allergens have demonstrated reduction in asthma symptoms, experts differ in their acceptance of this approach. Adverse reactions to immunotherapy—particularly bronchoconstriction—are more frequent among patients with asthma, especially those with poorly controlled asthma, than among patients who have allergic rhinitis. High-dose sublingual immunotherapy has been reported to be effective in patients with asthma, and this route avoids the risk of systemic reactions. However, studies suggest it is less effective than immunotherapy administered by subcutaneous injection.

Indoor air modification devices. The following measures are recommended:

• Vacuuming carpets once or twice a week to reduce accumulation of house dust. Patients who are sensitive to house dust should avoid using conventional vacuum cleaners and should avoid rooms where a vacuum cleaner is, or has just been, in use. If patients vacuum, they can use a dust mask, a central cleaner with a collection bag located outside the home, or a cleaner with a high-efficiency particulate air (HEPA) filter or a double bag.
• Using central air-conditioning. This prevents entry of outdoor allergens and reduces growth of house dust mites. 
• Use of a dehumidifier in areas of year-round high humidity (to reduce dust mite levels).

Humidifiers and evaporative (swamp) coolers are not recommended for use in the homes of patients with asthma who are sensitive to house dust mites.

Indoor air-cleaning devices are not effective substitutes for the measures described in the Table, although some of the devices (eg, electrostatic precipitating filters) can reduce airborne cat dander, mold spores, and particulate tobacco smoke.

OCCUPATIONAL EXPOSURES
Early recognition and control of exposures is critical in occupationally induced asthma, because the likelihood of complete resolution of symptoms decreases with time. Workplace exposure to sensitizing chemicals or dusts can induce asthma, which often persists after the exposure has ended. This condition should be distinguished from allergen- or irritant-induced aggravation of preexisting asthma. Acute exposure to gases, dusts, or fumes can cause reactive airway dysfunction, an asthma-like condition.

Diagnosis. Suspect occupational asthma if the patient reports a correlation between asthma symptoms and work, with improvement after a few days’ absence from the workplace. Since symptoms often begin several hours after exposure, the patient may fail to recognize the correlation. Serial peak flow records at work and way from work can provide confirmation.

In your evaluation, consider the following elements:
Potential for workplace-related symptoms. Determine whether the patient is exposed to recognized sensitizers (eg, isocyanates, plant or animal products) or irritants (eg, cold/heat, dust, humidity), or whether coworkers have similar symptoms.
Symptom patterns. Verify whether there is improvement during vacations or days off (this may take a week or more); whether the symptoms are immediate (less than 1 hour), delayed (generally 2 to 8 hours after exposure), or nocturnal; or whether initial symptoms occur after a high-level exposure (eg, spill).
Documentation of work-related symptoms. Ask the patient to do serial charting for 2 to 3 weeks, recording exposures, symptoms, and bronchodilator use, and measuring and recording peak flow every 2 hours while awake.
Immunologic tests and further confirmatory evaluations. Order as needed.

IRRITANTS
Patients with asthma of any severity should be queried about exposure to irritants (see Box).

Tobacco smoke. This is the most important environmental indoor irritant and is a major precipitant of asthma symptoms in both children and adults. Thus, it cannot be emphasized strongly enough that asthmatic patients should not smoke or be exposed to tobacco smoke.

Outdoor and indoor air pollution and irritants. Asthma symptoms may be precipitated by exposure to increased air pollution levels (especially respirable particulates, ozone, sulfur( dioxide, and nitrogen dioxide). Thus, asthmatic patients should avoid exertion or outdoor exercise insofar as possible when levels of air pollution are high.

Patients should also avoid exposure to fumes from unvented gas, oil, or kerosene stoves; wood-burning appliances or fireplaces; and sprays and strong odors, especially perfumes. All of these can irritate the lungs and may precipitate asthma symptoms. In addition, formaldehyde( and volatile organic compounds—which can arise from sources such as new linoleum flooring, synthetic carpeting, particleboard, wall coverings, furniture, and recent painting—are potential irritants.