Asthma and the Home Environment

More than 17 million persons in the U. S. are estimated to have asthma (CDC, 1998a). Among children, it is the most common chronic illness (NAS, 2000). A substantial body of research indicates that the prevalence and severity of asthma have increased dramatically over the last several decades in the United States and many other parts of the world (CDC, 1998b; Carter and Platts-Mills, 1998; Platts-Mills, 1998).
t Many researchers point to the home environment as an important factor in determining asthma risk (Custovic et al., 1998).
Data show children in the U.S. currently spend the overwhelming majority of their time indoors (USEPA, 1997a).
Common indoor allergen sources include dust mites, cockroaches & rodents, pets, mold, and SHS (Secondhand Smoke).
Exposure to house dust mite allergens in childhood has been linked to an increase in the risk of developing asthma, and numerous other allergens are associated with asthma exacerbation in sensitized individuals (NAS, 2000).
Other factors can exacerbate asthma symptoms, such as indoor pollutants (secondhand smoke), indoor combustion products, formaldehyde, VOCs, pesticides), outdoor pollutants that penetrate the indoor environment (sulfur oxides, ozone, particulate matter), cold air, exercise, and the presence of wood burning stoves and fireplaces.
The primary determinants of dust mite growth in homes are food source (i.e., skin scales), temperature, humidity and the availability of upholstered furniture, carpets, mattresses, and pillows (Vaughan and Platts-Mills, 2000).
Other features of houses that can increase levels of mite growth include poor ventilation, excess production of water in the house (e.g., humidifiers, unvented cooking), water leakage, poor cleaning habits, and being on the ground floor level (NAS, 2000).
The use of impermeable bedding covers combined with frequent washing of bedding materials has been shown to be effective in reducing house dust mite allergen levels in the bed (Vojta et al., 2001; Vaughan et al., 1999a).
The most effective coverings for bedding have been shown to be permeable to air and water vapor, bur tightly woven and impermeable to mites. In a study that tested the effectiveness of different “allergen proof” bedding encasement materials (Vaughan et al., 1999a), tightly woven fabrics.

Common eradication methods include:

  • Maintaining a relative indoor humidity less than 50%
  • Encasement of mattresses and pillows in covers (<10 µm in pore size) and washing of bedding in hot (<130°F) water
  • Removal of fitted carpets (especially in humid zones) or treatment with acaricides
  • Dry vacuuming and dry steam cleaning (carpets, floors, and upholstered furniture)
  • Removal of soft toys for children
  • Regular year round cleaning protocol

Cockroach & Rodent Allergens:
Cockroaches, like dust mites, thrive in temperate and humid regions, but they may also proliferate in northern states (Chapman et al., 1997). Research has indicated that cockroach allergens are generally more likely to be found at higher levels in multi-family homes, often in high-poverty regions of large metropolitan areas (Kitch et al., 2000; Arruda et al., 2001). Concentrations of cockroach allergen are typically highest in kitchens and bathrooms where food and water sources are plentiful. The humidity in a home may be an important factor in cockroach infestations for some species. These approaches may include: cleaning and limiting open food stuffs, eliminating water sources, selective rodenticide use, and sealing holes and cracks in the home.

Cat and dog allergens are carried on smaller airborne particles, and in contrast to dust mite and cockroach allergens, may remain suspended in the air for long periods of time (Chapman and Wood, 2001; NAS, 2000). Cat and dog dander may also be transported easily from room to room and deposited in high levels on the walls and other surfaces within the home (Chapman and Wood, 2001; NAS, 2000). Research has also indicated that clothing can be a major source of inhaled cat and dog allergens (O'Meara and Tovey, 2000). 

Molds can grow on water-affected building materials such as wood, insulation materials, cellulose in the paper backing on drywall, and glues used to bond carpet to its backing, as well as furniture, clothing, and dust and dirt. The primary factor affecting fungal growth in homes is moisture level. In general, most molds require fairly wet conditions (near saturation), lasting for many days, to extensively colonize an environment (NAS, 2000). Features of houses that can increase moisture levels and fungal growth include being on the ground floor level, poor ventilation, excess production of water in the house (e.g., humidifiers, unvented cooking), and water leakage or flooding. Molds are present in household dust and on surfaces. Research clearly indicates that exposure to mold plays a role in the exacerbation of asthma symptoms in sensitized individuals.




Montana State University Extension Service  ~  Taylor Hall   ~  Bozeman, MT  59717 
Phone: (406) 994-3451  ~  Fax: (406) 994-5417 
Questions, comments, or suggestions? 
t Native AIR (Asthma Intervention & Reduction)
This effort is funded by the 
U.S. Dept. of Housing & Urban Development - Healthy Homes & Lead Hazard Control