Dust Mite, Animal Allergy and Chemical Sensitivity

by National Institute of Health

(Page 4 of 7)

Dust Mite Allergy

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

House dust 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 Illustration of a dust mite. include dead dust mites and their waste products. These waste products, which are proteins, actually provoke the allergic reaction.

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 and materials such as 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, other allergens peculiar to an individual house or building.

Cockroaches are commonly found in crowded cities and in the southern United States. Certain proteins in cockroach feces and saliva also can be found in house dust. These proteins can cause allergic reactions or trigger asthma symptoms in some people, especially children. Cockroach allergens likely play a significant role in causing asthma in many inner-city populations.

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. Researchers have found, however, that the major allergens are proteins in the saliva. These proteins stick to the fur when the animal licks itself.

Urine is also a source of allergy-causing proteins, as is the skin. 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, 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 2 years or more to develop and may not decrease until 6 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 4 to 6 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 lived on the premises.

Chemical Sensitivity

Some people report that they react to chemicals in their environments and that these allergy-like reactions seem to result from exposure to a wide variety of synthetic and natural substances. Such substances can include those found in paints, carpeting, plastics, perfumes, cigarette smoke

Plants

Although the symptoms may resemble those of allergies, sensitivity to chemicals does not represent a true allergic reaction involving IgE and the release of histamine or other chemicals. Rather than a reaction to an allergen, it is a reaction to a chemical irritant, which may affect people with allergies more than others.

Diagnosis

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. Testing for allergies is the best way to find out if a person is allergic.

Skin tests

Allergists (doctors who specialize in allergic diseases) use skin tests to determine whether a person has IgE antibodies in the skin that react to a specific allergen. The allergist will use weakened extracts from allergens such as dust mites, pollens, or molds commonly found in the local area. The extract of each kind of allergen is injected under a person's skin or is applied to a tiny scratch or puncture made on the arm or back.

Skin tests are one way of measuring the level of IgE antibody in a person. With a positive reaction, a small, raised, reddened area, called a wheal (hive), with a surrounding flush, called a flare, will appear at the test site. The size of the wheal can give the doctor an important diagnostic clue, but a positive reaction does not prove that a particular allergen is the cause of symptoms. Although such a reaction indicates that IgE antibody to a specific allergen is present, respiratory symptoms do not necessarily result.

Blood tests

Skin testing is the most sensitive and least costly way to identify allergies. People with widespread skin conditions like eczema, however, should not be tested using this method.

There are other diagnostic tests that use a blood sample to detect levels of IgE antibody to a particular allergen. One such blood test is called the radioallergosorbent test (RAST), which can be performed when eczema is present or if a person has taken medicines that interfere with skin testing.

About the Author

NIH is the nation's medical research agency - making important medical discoveries that improve health and save lives. The National Institutes of Health (NIH), a part of the U.S. Department of Health and Human Services, is the primary Federal agency for conducting and supporting medical research.