Environmental Factors

Today, we spend ~90% of our time indoors, either at home or in the workplace. This move towards a sedentary indoor lifestyle may contribute towards the increase in asthma seen in Western societies over the past 30 years. Allergy is the price we pay for this comfortable lifestyle. The changes that we have made to our homes to make them more comfortable also enhance allergen exposure.

Central heating, fitted carpets, and insulation maintain warm temperatures and high humidity and reduce air ventilation. Humidity is one of the most important factors that affect mite growth. Reducing the relative humidity below 50% for 6 months of the year will kill dust mites.

High humidity causes mold growth and favors cockroach infestation. Even in areas of low humidity, indoor allergens other than dust mites are associated with asthma and allergic diseases. Mites can survive short periods of low humidity by “sealing” themselves off from the environment. They also burrow down into mattresses, carpet pile, and furnishings where the local microclimate enables them to survive.

EPA’s Office of Research and Development’s “Total Exposure Assessment Methodology (TEAM) Study” found levels of common organic pollutants to be 2 to 5 times higher inside homes than outside, regardless of whether the homes were located in rural or highly industrial areas. TEAM studies indicated that while people are using products containing organic chemicals, they can expose themselves and others to very high pollutant levels. Elevated VOC concentrations can persist in the air long after the activity is complete and use has stopped.

Properties of Allergens

  • Or put another way, what is it about mite feces, cockroach secretions and cat skin flakes that makes people have allergies? The property that these substances have in common is that they all contain allergenic proteins. Dust mite and cockroaches produce between 5 and 10 protein allergens. In several cases, the allergens are enzymes used by mites to help them digest food. They become allergens when excreted with the feces.
  • After being inhaled by humans, the allergens rapidly leach out of the feces and bind to allergic antibodies on mast cells. The allergenic proteins serve a useful function for mites, but cause misery for humans.
  • By measuring allergen proteins, exposure to one allergen can be directly compared with another. We can also obtain more precise measurements and estimate what level of exposure causes allergies to develop, and what level causes symptoms to occur. Laboratory-based tests have been developed for measuring the most important indoor allergen proteins. To assess allergen exposure in the home, a dust sample is collected from the bed, carpet, or sofa. This is done by attaching a collection device to the vacuum cleaner and vacuuming a square yard area of the bed/carpet/sofa for 2 minutes. The dust sample is sent to the lab, sieved, and suspended in a saline solution. The dust extract can then be tested for allergen content. Having your dust allergen tested, will enable the doctor to determine whether your level of exposure is significant. Several commercial laboratories now offer testing services for measuring indoor allergens. Enquire about these services with your doctor or with your local indoor air quality specialist. These tests can help you decide whether you need to spend money on allergen control procedures or products.
  • Avoidance of indoor allergens is recommended by the National Heart Lung and Blood Institute and by the American Academy of Allergy, Asthma & Immunology as the first step in treatment of asthma.
  • Clinical studies have shown that the lungs of asthma patients improve if allergen levels in the home are reduced. Two factors are essential for allergen avoidance to be successful. First, the procedures used need to be effective in reducing allergens levels in the home. Secondly, the avoidance procedures usually need to be carried out for several months in order to be most effective. Intermittent or superficial treatments usually do not work. It is important to try to reduce allergen levels in the home. First, to prevent people becoming allergic and, second, to reduce the symptoms of people who are already sensitive to the allergen.

The steps outlined above represent ideals that are best achieved if you are building a new home or moving into a home that you own. If you rent or lease property, it may be difficult to remove carpets or make changes to indoor humidity or ventilation. These steps may call for changes in lifestyle that may not be acceptable to all family members. Bearing these general allergen avoidance strategies in mind, let’s look at some additional measures that can be used to control indoor allergens.

Tips to Reduce Your Exposure

Reduce the relative humidity to below 50%.

This is easier said than done. In temperate climates, humidity can be reduced using central air conditioning systems or dehumidifiers. In climates with high outdoor humidity year-round, central air conditioning may help, but in most cases will not reduce the relative humidity below 50%.

Increase ventilation.

This is particularly important for cat and dog allergens which have high airborne concentrations. Increasing the air exchange rate in your house up to 5 air exchanges in one hour will significantly reduce exposure to these allergens.

Consider removing wall-to-wall carpets and replacing them with hardwood, vinyl or ceramic tile floors. Carpets are a tremendous reservoir of both dust mites and animal allergens. Animal allergens accumulate to levels that can be 100-fold higher in carpeted rooms than in non-carpeted rooms. Using a flooring system other than wall-to-wall carpets is an important part of allergen control. This does not mean that the living area has to be spartan or “carpet-free”. Throw rugs, runners, small oriental rugs and dhurries can be used for decorative purposes, especially if they are washable and cleaned regularly, or can be dry cleaned.

Wash bedding regularly.

This is important for dust mite, cat, and cockroach allergens. Ideally, the bedding should be washed weekly in hot water at a temperature of approximately 130°F.  Cover mattress and pillows in mite-proof coverings.