Indoor allergens like dust mites, family pets, and poor ventilation can make the home an indoor jungle for asthmatics.

By Tracey Mitchell, RRT, RPFT

The best way to prevent and control allergen-caused diseases such as asthma is to prevent exposure to the allergens. Avoidance of specific known allergens can dramatically improve asthma by reducing the cascade of symptoms and the severity of the disease. Because Americans spend more than 90 percent of their time indoors, it is important for health care practitioners to focus their investigation and intervention efforts on the inside environment. It is necessary for health care practitioners to develop a strategy for identifying environmental triggers indoors and a practical plan for environmental control and avoidance that the patient can adopt.

Searching for Clues

Intensive investigating is often required to uncover the environmental culprit causing recurrent asthma episodes. Methods used for detecting a person’s specific asthma trigger(s) include taking a complete medical history and performing skin tests and pulmonary function tests. It may be necessary to perform environmental evaluation and testing to determine the cause or level of allergen in a home.

A thorough medical history of the patient is the primary diagnostic tool. A complete medical history includes information about the patient’s general overall health as well as specifics about his/her family history; past medical hospitalizations and surgeries; recent changes in symptoms; known allergies and suspected triggers; and current medications. Information regarding nontraditional therapies such as acupuncture and chiropractic manipulation and use of over-the-counter remedies should also be considered part of the patient’s medical history. This information is normally obtained by having the patient complete a questionnaire, then confirming the written answers by verbally asking for clarification and more details. Performing an extensive investigation of the patient’s history is the first step in designing an environmental control strategy that is practical, effective, and comprehensive.

Because allergies are associated with asthma more than 50 percent of the time, allergy testing is often necessary to focus environmental interventions on specific asthma triggers. Allergy testing should target those allergens identified as suspected triggers in the patient questionnaire and should be conducted by a board-certified allergist. Once allergies are confirmed through allergy testing, a specific and targeted plan for allergen avoidance should be designed with and for the patient.

One problem concerning allergy testing is the lack of well-characterized, standardized reagents for some allergen extracts. Dust mite and cat extracts contain standardized amounts of major allergen, but others, such as fungi, are not yet standardized. It may be appropriate to also include pulmonary function tests and/or the methacholine challenge test in the investigation for asthma triggers. These tests will determine the degree of obstruction and decrease in lung function, and may be necessary to make a differential diagnosis of asthma.

Daily peak expiratory flow readings are usually helpful for diagnosis as well as long-term management of asthma. A written daily diary of exposure and symptoms that may be incorporated with the daily peak expiratory flow chart the patient is already recording is another beneficial tool for asthma management. This diary will correlate exposure to allergens and irritants with symptoms such as coughing and wheezing, helping the practitioner clearly see the relationship between exposure to certain environmental triggers and asthma episodes.


An environmental evaluation is a valuable tool in the development of an asthma prevention strategy. Environmental evaluation involves assessing the place where the asthma patient spends the majority of his/her time and where he/she has some control over the surroundings. This usually means assessing the person’s home and, depending on his/her triggers, focusing specifically on the bedroom. When doing home evaluations, therapists should rely on their senses to identify the presence of triggers, their sources, and potential contributors to indoor air quality problems. Look for signs of water damage or evidence of indoor pets; note any strange or strong odors; note the temperature and humidity in the room. These are all indications of poor indoor air quality and are potential asthma triggers.

Environmental testing or monitoring can help determine the cause and amount of allergen a patient is exposed to at home. Depending on what allergen you are measuring, samples are collected either from ambient air in one or more rooms of the house or from potential allergen reservoirs. Samples should be collected in the area where the patient spends the most time, typically a bedroom or living room, or any place where the patient experiences symptoms.

There is a need for improved, standardized methods of collecting and analyzing indoor allergen samples; therefore, it is difficult to access the quality of the sample testing, and testing for many pollutants can be expensive. Before testing, consult your state and local health departments, which should have experience handling indoor air quality problems and dealing with indoor environmental triggers.

Going Inside

The major sources of indoor allergens in the United States are house dust mites, molds or fungi, animal dander from cats and dogs, and cockroaches. When performing a home assessment, one should keep these common sources in mind as well as the results of the patient’s skin test. Again, the bedroom is one area where steps to reduce allergen exposure can have a dramatic positive effect on the health of an asthma sufferer.

Basic Environmental Control

In general, the most effective and often most cost-efficient way to prevent exposure to asthma triggers is to eliminate the source or reduce its concentration. The following are specific strategies to control each of the most common indoor allergens.

Dust Mites

These microscopic animals, found in household dust, feed on flakes of human skin and thrive in humid, damp conditions. They are usually abundant in the bedroom, particularly in mattresses and pillows. People who are allergic to dust mites should use allergen-proof encasings on pillows and mattresses, wash all bedding in hot (130 degrees F) water, and avoid soft, fabric-covered furnishings that accumulate dust. Reducing relative humidity to below 500and vacuuming with a high-efficiency particulate air (HEPA) filter may be helpful in reducing the number of allergen particles.


These pests have recently been identified as a common source of indoor allergen, especially in inner-city dwellings. Cockroach allergen can be found throughout the house, but the highest levels are usually found in the kitchen. Their fecal material and saliva cause allergic reactions.

To rid a home of cockroaches, one must apply integrated pest management. This involves thoroughly cleaning and removing all cockroach bodies and residues, storing food in tightly sealed containers, repairing leaks, and keeping all surfaces clean and dry. Keeping food out of the bedroom helps reduce exposure. Instead of spraying, reduce exposure to toxic pesticides by using bait traps under sinks and behind appliances and cabinets, and reduce pest entryways by caulking cracks and crevices.

Molds and Fungi

These triggers grow in damp, humid environments. Molds reproduce by forming spores and sending them into the air. Mold is often found in basements and showers or any room with a leaky roof or water damage. If mold is a problem, reduce humidity and prevent condensation by increasing ventilation, removing any standing water and water-damaged materials, and repairing any leaks. Clean moldy areas with a bleach-and-detergent mixture, being sure to wear a protective mask and increase ventilation to reduce fumes. A dehumidifier may be helpful, but always follow the manufacturer’s instructions for cleaning and maintenance because a dirty humidifier can aggravate allergy and asthma symptoms. Avoid having the person with asthma sleep in a basement bedroom.


Up to 60 percent of US households own a pet. Animal dander-dry flakes of skin that an animal sheds with its fur-contributes significantly to asthma episodes. The dander, along with proteins in saliva, make cats a particularly potent asthma trigger. It is thought that the allergen is transported on clothes so that many households without a cat contain surprisingly high levels of allergens. Removing the pet from the house is the best way to avoid animal dander. Once a cat is removed, it takes several months for the level of cat allergen to decrease in the home. Animals should, at the very least, be kept out of the bedroom. Washing the animal weekly can help temporarily reduce the amount of dander and allergen produced.

Environmental Tobacco Smoke (ETS)

Although not an allergen, ETS is a strong irritant and a common asthma trigger. ETS, also called secondhand smoke, is a mixture of smoke that comes from a cigarette, cigar, or pipe and the smoke exhaled by the smoker. It is a complex mix of more than 4,000 compounds, more than 40 of which are known carcinogens. The EPA estimates that up to 1 million children with asthma experience exacerbations triggered by ETS.

Smoking should never be allowed inside the house of a person who has asthma. If smoking inside cannot be avoided, open windows or use exhaust fans to increase the ventilation indoors and decrease exposure.

Ensuring Compliance

Once a patient’s asthma triggers are determined, the difficult part of treatment begins. Often patients are overwhelmed because they are given a list of interventions for all of their environmental triggers and little guidance on how to go about making the suggested changes. Practitioners need to consider economic, educational, and ethnic factors in addition to environmental risk factors when designing an environmental intervention program. During the evaluation and counseling, it is important for practitioners not to appear judgmental. Make suggestions for reducing exposure to asthma triggers in the home, but be cautious not to give absolutes and ultimatums.

There are emotional issues for health care practitioners to consider as well. Sometimes tough decisions have to be made. If the family cat is responsible for frequent asthma episodes, it may be time to find a new home for this beloved family member. Practitioners should be sensitive to these issues and be supportive of the patient during this difficult transition. Effecting behavior change requires patient education and compliance. To achieve patient acceptance for avoidance of triggers, practitioners should develop an educational program that is practical and appropriate for the patient.

Each patient needs an individualized environmental intervention program. The plan should meet their specific needs, address their asthma triggers, and fit their lifestyle. Practitioners should keep this in mind and provide patients with options and a flexible plan for decreasing exposure to triggers and improving asthma symptoms.


Tracey Mitchell, RRT, RPFT, is an environmental scientist at the US Environmental Protection Agency in Washington, DC. The views expressed here are her own and not necessarily those of the EPA.


1. Pope AM, Patterson R, Burge H, eds. Indoor Allergens: Assessing and Controlling Adverse Health Effects. Washington, DC: National Academy of Sciences, National Academy Press; 1993.

2. The Inside Story: A Guide to Indoor Air Quality. Washington, DC: US Environmental Protection Agency, US Consumer Product Safety Commission; 1993:1