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Many allergens are in the air. Worldwide, airborne allergens cause the most problems for people with allergies. The respiratory symptoms of asthma, which affect approximately 11 million Americans, are often provoked by airborne allergens.
Common Airborne Allergens
Pollen is a mass of tiny grains produced by plants to reproduce. Among North American plants, weeds are the most prolific producers of allergenic pollen. Ragweed is the major culprit, but other important sources are sagebrush, redroot pigweed, lamb's quarters, Russian thistle (tumbleweed), and English plantain. Grasses and trees, too, are important sources of allergenic pollens. Although more than 1,000 species of grass grow in North America, only a few produce highly allergenic pollen.
The allergy to pollen is known as hay fever.
Molds are a kind of fungi. The seeds or reproductive pieces of fungi are called spores. Spores differ in size, shape, and color among types of mold. They float in the air like pollen. When inhaled, tiny mold spores may cause allergic rhinitis. Because they are so small, mold spores also can reach the lungs.
Molds can be found wherever there is moisture, oxygen, and a source of the few other chemicals they need. In the fall, they grow on rotting logs and fallen leaves, especially in moist, shady areas. In gardens they can be found in compost piles and on certain grasses and weeds. Hot spots of mold growth in the home include bathrooms, damp basements and closets.
Dust mites are microscopic organisms that live 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.
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.
The signs and symptoms of airborne allergies are familiar to many:
In people who are not allergic, the mucus in the nasal passages simply moves foreign particles to the throat, where they are swallowed or coughed out. But something different happens in a person who is sensitive to airborne allergens. In sensitive people, as soon as the allergen lands on the lining inside the nose, a chain reaction occurs that leads the mast cells in these tissues to release histamine and other chemicals. The powerful chemicals contract certain cells that line some small blood vessels in the nose. This allows fluids to escape, which causes the nasal passages to swell - resulting in nasal congestion. Histamine also can cause sneezing, itching, irritation, and excess mucus production, which can result in allergic rhinitis. Other chemicals released by mast cells, including cytokines and leukotrienes, also contribute to allergic symptoms.
Some people with allergy develop asthma, which can be a very serious condition. The symptoms of asthma include
The shortness of breath is due to a narrowing of the airways in the lungs and to excess mucus production and inflammation. Asthma can be disabling and sometimes fatal. If wheezing and shortness of breath accompany allergy symptoms, it is a signal that the airways also have become involved.
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.
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.
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.
If you could, the best way to handle allergies is to avoid the allergen. If you cannot adequately avoid airborne allergens, the following medicines may be used:
As the name indicates, an antihistamine counters the effects of histamine, which is released by the mast cells in your body's tissues and contributes to your allergy symptoms. For many years, antihistamines have proven useful in relieving itching in the nose and eyes; sneezing; and in reducing nasal swelling and drainage.
Topical Nasal Steroids
Topical nasal steroids are anti-inflammatory medicines that stop the allergic reaction. In addition to other helpful actions, they decrease the number of mast cells in the nose and reduce mucus secretion and nasal swelling. The combination of antihistamines and nasal steroids is a very effective way to treat allergic rhinitis, especially if you have moderate or severe allergic rhinitis. Although topical nasal steroids can have side effects, they are safe when used at recommended doses.
Cromolyn sodium is a nasal spray that in some people helps prevent allergic rhinitis from starting. When used as a nasal spray, it can safely stop the release of chemicals like histamine from mast cells. It has few side effects when used as directed and significantly helps some people manage their allergies.
Immunotherapy, or a series of allergy shots, is the only available treatment that has a chance of reducing your allergy symptoms over a longer period of time. You would receive subcutaneous (under the skin) injections of increasing concentrations of the allergen(s) to which you are sensitive. These injections reduce the level of IgE antibodies in the blood and cause the body to make a protective antibody called IgG.
About 85 percent of people with allergic rhinitis will see their hay fever symptoms and need for medicines drop significantly within 12 months of starting immunotherapy. Those who benefit from allergy shots may continue it for 3 years and then consider stopping. While many are able to stop the injections with good results lasting for several years, others do get worse after the shots are stopped.
One research study shows that children treated for allergic rhinitis with immunotherapy were less likely to develop asthma. Researchers need to study this further, however. As researchers produce better allergens for immunotherapy, this technique will be become an even more effective treatment.