The major sources of indoor allergens in the United States are house dust mites, fungi and other microorganisms, domestic pets (cats and dogs), and cockroaches. The allergens produced by these organisms become airborne and can cause the allergic diseases mentioned previously, such as hay fever, asthma, and hypersensitivity pneumonitis.

The dust mite, a microscopic organism that lives primarily in carpeting and on mattresses and upholstery, produces several of the most common residential allergens. Although there are regional and local differences in dust mite concentrations, they are thought to be one of the most important allergenic causes of childhood asthma. Dust mite allergens, which have been purified and characterized, are contained in fecal balls that accumulate in bedding and on other surfaces.

Fungi release allergen-containing spores and other products indoors and outdoors. Although there are thousands of different fungi that can contaminate indoor air, purified allergens have been recovered from only a few; none has been completely characterized. Fungus spore allergens are known to cause hay fever, asthma, and hypersensitivity pneumonitis; other fungal products can be irritating or toxic, possibly exacerbating allergic conditions.

Allergens released by house pets have been purified and characterized and are an important cause of allergic rhinitis and asthma. Research has shown that cat allergens become airborne on very small particles and remain in buildings long after the cat has departed.

Cockroach allergen (which has also been purified and characterized) is derived from the insect's body parts and feces. In many inner-city areas, cockroach allergens probably play a significant role in the development of allergic rhinitis and asthma.

In addition to allergens derived from biological sources, some reactive allergenic chemicals can cause allergic disease. In general, these chemicals are more prevalent in the industrial workplace than the home. However, a limited number of household products may contain immunogenic agents (e.g., isocyanates in bathtub refinishing products).

The best way to prevent and/or control allergen-caused disease is to prevent exposure to the allergenic agent. Avoidance of specific allergens can lessen the probability of initial sensitization and, for individuals with known sensitivity, it can improve their condition dramatically by reducing the cascade of symptoms.

The bedroom is one area where steps to reduce exposure to allergens can have a beneficial effect on health. In the case of dust mite allergen, for example, covering mattresses and pillows with impermeable materials is an effective way to limit exposure (Box 1). Such avoidance measures are important tools for managing allergic disease and asthma caused by dust mite allergen.

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