House dust is a complex mixture of, among other things lint, dander, fibers, mites, mite-derived feces, and insect parts. Overwhelming evidence points to the house dust mite, Dermatophagoides (literally, the skin eaters, because they feed on human skin dander), as the principal allergy-provoking element of house dust. These arachnids encase their feces in an intestinal enzyme-coated material that is thought to be the primary allergen for provoking the symptoms of perennial rhinitis and asthma.

Since mite fecal balls are relatively large and heavy, they float only very briefly in the air and settle quickly within "dust traps" such as carpets, bedding, and upholstery. Disturbing these sites, as for example during vacuuming, may result in a thirty-minute period of markedly increased airborne allergens and the possibility of eliciting inhalation allergy in sensitive individuals. Prevention and treatment therefore consist of dust-proofing the home environment as much as possible. This means eliminating carpets and other sites where mites thrive, emptying closets, encasing bedding, and frequently laundering curtains and bedding with hot water.

Cockroaches, the endemic pests of the urban dweller, are another major source of inhalation allergies. When these insects die naturally or are exterminated, their bodies slowly turn to a powdery material that becomes airborne. In addition, just as in the case of house mite feces, cockroach feces can also provoke allergy symptoms. Allergies to cockroaches should be considered in any urban dweller who suffers symptoms of perennial allergic rhinitis or asthma.

In theory, prevention and treatment of the problem is simple:
Eliminate the source. Unfortunately, cockroaches are extremely hardy organisms. For example, we know that one cockroach can survive on a tiny drop of water for a whole year. To date the only consistently effective measure for reducing exposure is periodic commercial extermination.