Lourdes Rosales-Guevara, MD  
To achieve successful asthma control and effective long-term management, it is important to identify allergens, irritants, and pollutants that trigger asthma so asthma flare-ups can be prevented. Making changes in individual and family behavior and complying with treatment regimens also play important roles in the successful control of asthma. Resources on asthma can be found in the sidebar article.

Allergens
Allergens are substances capable of inducing an allergy or a specific hypersensitivity reaction. The most important step in controlling allergen-induced asthma is reducing exposure to the agents to which the patient might be sensitive. Reducing exposure will help prevent exacerbations of asthma.

For children, allergens might be encountered at home, in their classroom or day care center, on the playground, during family moves or house renovations, and during weather changes and seasonal variations.

Adults are affected by the same allergens that affect children. Adults can also be exposed to allergens in the workplace.

Cockroach Allergen: This allergen is more of a problem for people with asthma who live in low-income housing. The severity of asthma in these patients is directly proportional to the levels of cockroach allergen in their bedrooms.

Animal Allergens: All warm-blooded pets, including birds and small rodents, can cause allergic reactions in sensitive patients because of dander and body secretions (urine, feces, and saliva). Dander is small scales from the hair, skin, or feathers of animals.

House Dust Mites Allergen: The survival of mites depends on increased relative humidity and on human dander. Increased concentrations of mites are in all bedclothes (dust covers, pillows, and mattresses), upholstered furniture, carpets, clothes, and stuffed toys.

Pollens: Pollen from trees, grass, or weeds can be a problem, especially during spring and fall seasons.

Indoor Mold: Indoor mold can be found where humidity levels are high, such as in bathrooms (especially bathrooms without windows and bathrooms with leaking faucets) or basements, and in homes where dampness is a problem. Inspecting rooms for molds, such as looking under old carpets, might reveal areas covered with mold.

Irritants
Fumes From Wood or Gas Stoves: Malfunctioning stoves (gas, oil, kerosene, or wood), fireplaces, or strong odors can irritate the lungs, precipitating asthma symptoms.

Environmental Tobacco Smoke (ETS): ETS is a major precipitant of asthma symptoms and the most important and preventable indoor environmental irritant. ETS exposure is associated with early onset of asthma symptoms, increases in asthma exacerbations, consequent increased use of medication, and lengthened recovery periods. Prenatal exposure to ETS can adversely impact a child. Maternal smoking during pregnancy (as few as 10 cigarettes per day) has been associated with an increased risk of the child developing asthma later in life.

To help control exposure to cockroach allergen

Discard food leftovers: exposed food or garbage residue can attract cockroaches.

Limit eating areas to dining room and/or kitchen.

Use traps instead of chemical agents for pest control. When chemical agents are applied, make sure that sensitive patients are kept out of the area. Ventilate the premises for several hours or until the chemical odor is gone.
 
To help control exposure to animal allergens

Remove the pet from the house (preferred). If removal is not feasible, keep the pet out of the patient’s bedroom and keep the door closed.

Remove carpets and upholstered furniture from the patient’s bedroom or family home or isolate the pet from these items.

Wash the pet and change litter frequently (once a week) to decrease the amount of dander and/or body secretions from its hair or feathers.
 
To help control exposure to, and levels of, house dust mites

Use allergen-impermeable mattress and pillow covers, and damp-wipe them clean once a week.

Wash stuffed toys and bedclothes in hot water (temperature of 130°F [54°C]) to kill the mites.

Use a damp wipe to clean the patient’s bedroom furniture.

Use a high-efficiency particulate air (HEPA) filter vacuum cleaner.
 
To help control pollen allergy

Stay indoors with the windows closed during peak pollen seasons.

Clean air filters frequently.

Use antiallergic medical control.
 
To help control indoor mold

Avoid using humidifiers. Maintain indoor humidity at <50%.

Fix leaking faucets and eliminate standing water.

Do not allow sensitive patients in problem areas such as the basement.
 

To help control exposure to fumes from wood or gas stoves

Ensure proper functioning of stoves and fireplaces.

Use kitchen vents when cooking.
 

To help control exposure to environmental tobacco smoke

Parents who smoke should quit; if they are unable to quit, they should smoke outside—never in the home or in the family car.

If children attend day care, ensure that day care staff do not smoke indoors.
 
 

Outdoor Pollutants
Nitrogen Dioxide (NO2): In contrast to the other pollutants in this section, NO2 is both an indoor and outdoor air pollutant. Sources of indoor NO2 include malfunctioning gas stoves, furnaces, fireplaces, and kerosene space heaters. The effects of NO2 are thought to be due to long-term, low-level exposure. NO2 exposure that occurs when the patient is exercising or running might be more irritating to airways than exposure that occurs when the patient is not exercising.

Particulate matter (PM10 and PM2.5): Particulate matter is a mixture of solid particles and liquid droplets. The sources and potential health effects of particulate matter are different for the two sizes.

PM10, particulate matter 10 micrometers (µm) in aerodynamic diameter, is associated with exacerbation of existing asthma. Sources of PM10 include dust and street sand from crushing or grinding (i.e., construction work), vehicle exhaust, and smoke from burning wood.

PM2.5, particulate matter  2.5 µm in aerodynamic diameter, penetrates deeper into the lung, thus producing greater health effects. PM2.5 can precipitate asthma symptoms. Sources of PM2.5 include industrial and residential combustion, vehicle exhaust, and atmospheric reactions between gases (SO2 and NO2) and volatile organic compounds (VOCs).
Ozone (O3): O3 is the most potent irritant of the outdoor air pollutants. Its effect is immediate. O3 is suspected to induce or enhance the inflammatory response of the respiratory system. In the United States, a large fraction of ambient O3 is the product of photochemical reactions between various nitrogen oxides (NOx) and VOCs emitted from vehicles.

Sulfur Dioxide (SO2): SO2 is highly soluble. The nasal mucosa can fail to remove SO2, leading to upper airway irritation and subsequent penetration into the lung tissue. Greater exposure to SO2 might occur in persons who have asthma and who exercise. SO2 levels have been decreasing over the last 15 years, so it is unlikely that SO2 alone is responsible for the recent increases in the prevalence of asthma.

Outdoor mold: Outdoor mold can be found in shady, damp areas or places where leaves or other vegetation are decomposing. In warmer states, mold spores begin to show early in spring; levels of spores peak in July. In colder states, the peak for mold spores occurs during the fall. Children playing outside or adults raking leaves might be exposed to those spores. Molds can be found year-round outdoors in the South and on the West Coast.

Conclusion
Various environmental factors can trigger exacerbations of asthma. Interventions are available to mitigate these factors. Identifying possible asthma triggers and taking preventive action to reduce those triggers are imperative to achieving successful asthma control and effective long-term management.