From Vincent Iannelli, M.D.,
Your Guide to Pediatrics.
FREE Newsletter. Sign Up Now!

About.com Health's Disease and Condition content is reviewed by Kate Grossman, MD

Dust mite allergy is an allergy to a microscopic organism that lives in the dust that is found in all dwellings and workplaces. Dust mites are perhaps the most common cause of perennial allergic rhinitis. Dust mite allergy usually produces symptoms similar to pollen allergy and also can produce symptoms of asthma.

What is house dust?

Rather than a single substance, so-called house dust is a varied mixture of potentially allergenic materials. It may contain fibers from different types of fabrics; cotton lint, feathers, and other stuffing materials; dander from cats, dogs, and other animals; bacteria; mold and fungus spores (especially in damp areas) ; food particles; bits of plants and insects; and other allergens peculiar to an individual home.

House dust also contains microscopic mites. These mites, which live in bedding, upholstered furniture, and carpets, thrive in summer and die in winter. In a warm, humid house, however, they continue to thrive even in the coldest months. The particles seen floating in a shaft of sunlight include dead dust mites and their waste-products. These waste-products, which are proteins, actually provoke the allergic reaction.

Waste products of cockroaches are also an important cause of allergy symptoms from household allergens, particularly in some urban areas of the United States.

Animal Allergy

Household pets are the most common source of allergic reactions to animals. Many people think that pet allergy is provoked by the fur of cats and dogs. But researchers have found that the major allergens are proteins secreted by oil glands in the animals' skin and shed in dander as well as proteins in the saliva, which sticks to the fur when the animal licks itself. Urine is also a source of allergy-causing proteins. When the substance carrying the proteins dries, the proteins can then float into the air. Cats may be more likely than dogs to cause allergic reactions because they lick themselves more and may be held more and spend more time in the house, close to humans.

Some rodents, such as guinea pigs and gerbils, have become increasingly popular as household pets. They, too, can cause allergic reactions in some people, as can mice and rats. Urine is the major source of allergens from these animals.

Allergies to animals can take two years or more to develop and may not subside until six months or more after ending contact with the animal. Carpet and furniture are a reservoir for pet allergens, and the allergens can remain in them for four to six weeks. In addition, these allergens can stay in household air for months after the animal has been removed. Therefore, it is wise for people with an animal allergy to check with the landlord or previous owner to find out if furry pets had lived previously on the premises.

Chemical Sensitivity

Some people report that they react to chemicals in their environment and that these allergy-like reactions appear to result from exposure to a wide variety of synthetic and natural substances, such as those found in paints, carpeting, plastics, perfumes, cigarette smoke, and plants. Although the symptoms may resemble some of the manifestations of allergies, sensitivity to chemicals does not represent a true allergic reaction involving IgE and the release of histamine or other chemicals.

Diagnosing Allergic Diseases

People with allergy symptoms, such as the runny nose of allergic rhinitis, may at first suspect they have a cold--but the "cold" lingers on. It is important to see a doctor about any respiratory illness that lasts longer than a week or two. When it appears that the symptoms are caused by an allergy, the patient should see a physician who understands the diagnosis and treatment of allergies. If the patient's medical history indicates that the symptoms recur at the same time each year, the physician will work under the theory that a seasonal allergen (like pollen) is involved. Properly trained specialists recognize the patterns of potential allergens common during local seasons and the association between these patterns and symptoms. The medical history suggests which allergens are the likely culprits. The doctor also will examine the mucous membranes, which often appear swollen and pale or bluish in persons with allergic conditions.