Dust mites are reported to be the most common cause of allergy and asthma in North America. They are small organisms (not visible to the unaided eye) that live on partially decomposed human skin scales. As such, they live where humans live and are found most abundantly in our bedrooms and living/family room areas (where we spend most of our time). Though they look somewhat like insects, they are arachnids. As such, they are closely related to spiders and ticks.

As dust mites feed on human skin scales, they excrete wastes which are described as fecal pellets. Digestive enzymes in these waste materials are antigenic--they have the potential of causing immunological sensitization in potentially sensitive individuals. Once sensitized an individual can develop allergy symptoms or even asthmatic attacks on exposure to house dust contaminated with dust mite allergens.

Dust mites must obtain the water they need from air around them. As such, they do particularly well where relative humidity levels are high. They need a minimum relative humidity of 70% to survive and proliferate. Such relative humidities only occur in room air during rainy, damp weather and in very damp houses.

Fortunately for dust mites, high relative humidities needed for survival occur in our beds (where the moisture comes from our bodies) and at floor level (particularly in carpeting) where cooler temperatures cause humidity levels to rise into the critical mite-supporting range.

The use of wall-to-wall carpeting has been a big boon for dust mite populations. It serves to catch debris like skin scales which provide food for mites and provides an environment near floor level where high humidity levels can exist. Carpeting restricts air movement to the floor so that cooler temperatures and higher humidity levels are maintained.

Without humidities in the critical range, dust mites cannot thrive and populations will remain low. One can control dust mites by directly or indirectly controlling relative humidity conditions in one's home. There are several ways that this can be achieved. One of the simplest ways is to air-condition your home during summer months in northern states and for a more extended period in Gulf states such as Florida, Alabama, Mississippi, Louisiana, and the south coast of Texas. Air-conditioning does double duty; it cools and dehumidifies. As such, it reduces the amount of moisture that is delivered to cooler floor surfaces and thus reduces relative humidity below the critical 70% range. The use of air-conditioning has been shown to be an effective means of controlling dust mite populations.

Another way of controlling dust mites is to remove carpeting in the bedroom of dust-mite sensitive patients and replace with either hardwood flooring or vinyl. Dust mites cannot thrive on either surface because environmental conditions are too harsh. Additionally hardwood and vinyl surfaces are much easier to keep clean of the organic dust that provides mites with their food supply.

There are a variety of other approaches to controlling dust mites; their presentation will have to wait until another posting on this site.