Indoor Allergen Control Measures: A Practical Summary

By Peter B. Boggs, MD

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The Five Common Indoor Allergens:
Effective Remediation Measures

Dust Mites

The house dust mite is the most important indoor allergen (Der p 1). It is ubiquitous in most humid areas. Although 13 species of house dust mite have been identified, only three are common in homes: Dermatophagoides farinae, Dermatophagoides pteronyssinus, and Euroglyphus maynei. Most mite infestations in the United States are caused by D farinae or D pteronyssinus; one species generally dominates in a home. Environmental control measures for house dust mites have been extensively reviewed^6,7 (see also "A Final Word" and American Academy of Allergy, Asthma, and Immunology handouts 1 and 2).

The phrase "snug as a bug in a rug" is a fitting description of the house dust mite's relationship to us and our living/working environments. Their basic needs—food, shelter, and a water supply—are easily met in the safety of our living spaces. Their main food sources are shed skin cells and the variety of organic debris commonly associated with house dust. They are sheltered by the nature of where they reside: deep in carpets, in beds, and in upholstered furniture. Mites exchange water, oxygen, and carbon dioxide through their general body surface, so water needs are met when the relative humidity is > 50%. The latter is easily accomplished in humid geographic regions and in homes with carpet and padding installed over a concrete foundation.

Remediation measures for house dust mite allergen (Der p 1) exposure can be divided into those that are highly effective (first-line or priority measures) and those that are only somewhat effective (second-line or alternative measures) (Table 1). The highly effective measures should be first priority in any remediation program and include encasements for pillows, mattresses, and box springs; hot (> 130°F) water washing of bedding once a week; removal of close contact reservoirs (stuffed toys); and avoidance of basements and other highly humid spaces as living areas.

Encasement of the pillows, mattresses, and box springs provides the simplest and most effective barrier to house dust mite exposure. Encasements shown to be effective barriers to mite allergen are readily available through mail-order houses (Table 2). Washing bedding once a week in hot water will both kill mites that have accumulated since the last washing and remove mite allergen. Caution is advised with such washing as water at this temperature is a scalding hazard. Adding detergents only slightly increases the efficiency of cleaning.19 Dry cleaning and tumble drying will both kill mites, but are less effective in the removal of mite allergen than wet cleaning.^20,21

Vacuuming removes bulk dust from the carpet, bed, and upholstered furniture, but does not kill mites and does not change the concentration of mite allergen per gram of settled dust.²² On the other hand, steam cleaning of the carpet and bed has been shown to be effective in both killing mites and reducing mite allergen.²³

Because the house dust mite allergen (Der p 1) particles become airborne only with significant disturbance and are carried on relatively large particles (10 to 20 mm), they are able to remain in the air for only a relatively short period of time (hang-time is < 30 min). Hence, most dust mite allergen exposure is the result of close contact (beds, stuffed toys). The second major exposure to dust mite allergen comes on vigorous disturbance of their habitat such as during vacuuming and cleaning.

Measures that have shown some effectiveness but are currently felt to be less effective than essential measures include controlling the humidity in the home (40 to 50% relative humidity); removing carpet from primary living areas and replacing it with polished surfaces; replacing draperies with easily cleanable surfaces; and replacing fabric furniture with vinyl or leather.^3,5,7 A variety of chemical agents (acaricides and denaturants) are available, but have not been shown to be particularly effective in reducing mite allergen.²⁴ Apparently an active compound in the laboratory does not equate with good results in the home.

The threshold levels for sensitization and exacerbation of asthma are 2 mg/g and 10 mg/g, respectively.²⁵

Caveats. House dust mites are microscopic and hence do not provide the visual clues important in gaining commitment to remediation programs. Additionally, mite-allergic people generally do not experience exacerbations during short visits (a few hours) in homes heavily infested with mites, in contrast to the cat-allergic person who visits a home with an indoor cat. These observations reflect the importance of skin testing to confirm IgE sensitization and the identification of allergen(s) present in the patient's house dust.

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