Allergies: Causes, Diagnosis, Treatment
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One of the marvels of the human body is that it can defend itself against harmful invaders such as viruses or bacteria. In some people, the body reacts to harmless substances such as dust, mold or pollen by producing an antibody called immunoglobulin E (IgE). When patients with one of the allergic diseases (such as rhinitis or asthma) are exposed to these substances, the immune system then rallies its defenses, launching a host of complex chemical weapons to attack and destroy the supposed enemy. In the process, some unpleasant and, in extreme cases, life-threatening symptoms may be experienced.
Hundreds or even thousands of ordinary substances can trigger allergic reactions. These are called “allergens.” Among the most common are plant pollens, molds, household dust (dust mites), animal dander, industrial chemicals, foods, medicines and insect stings.
An allergic reaction may occur anywhere in the body, but usually appears in the skin, eyes, lining of the stomach, nose, sinuses, throat and lungs — places where special immune system cells are stationed to fight off invaders that are inhaled, swallowed or come in contact with the skin.
Allergies can affect anyone, regardless of age, gender, race or socioeconomic status. While it’s true that allergies are more common in children, they can occur for the first time at any age or, in some cases, recur after many years of remission.
Although the exact genetic factors are not yet understood, the tendency to allergies, as well as to allergic disease, is linked to heredity.
The best first step in the diagnosis of allergies is a thorough health history and physical examination. If you have allergy symptoms that occur in association with exposure to certain things, that is highly significant. Allergy diagnostic tests, such as skin tests or blood tests, provide similar information and merely confirm what your health history tells the doctor. If your doctor were to rely exclusively on the results of skin or blood tests (without history and physical examination), you could be diagnosed as having an allergic problem that you don’t necessarily have.
Skin tests, in most situations, are preferable because (1) the results are available immediately, (2) they are less expensive and (3) they are more sensitive to subtle allergies.
A blood test is appropriate in certain situations, particularly when you (1) cannot suspend antihistamine therapy which can inhibit skin tests, (2) have widespread skin disease making skin testing difficult, (3) are so sensitive to the allergen that the test might be risky or (4) cannot be skin tested for some other reason.
Like all medical treatments, allergy shots (immunotherapy) can have side effects. Your doctor will discuss this with you in detail. Under no circumstances should you consider allergy shots without at least an attempt at avoidance of the troublesome allergen. For instance, cat allergy shots are no substitute for cat avoidance. Some allergens, though, such as grass pollen, are almost unavoidable.
Why is it that frequent exposure to an allergen can increase sensitivity and cause allergic reaction, yet repeated exposure to an allergen in allergy shots helps build ups immunity?
Regularly scheduled, repeated exposure to small amounts of an allergen can lead to immunity, whereas infrequent and erratic exposure does not confer immunity but increases the likelihood of producing allergen sensitization.
Irregular exposure to allergens can lead to the production of antibodies (called IgE-mediated antibodies). The presence of these antibodies, when exposed to an allergen can lead to an allergic reaction.
In allergy shots or immunotherapy, the allergen exposure is closely regulated and given on a scheduled basis. Small amounts of allergens are given over a period of time to build up to maintenance doses. This leads to the production of blocking antibodies (called IgG antibodies) and a decrease in the level of allergic or IgE-mediated antibodies.
Source: American College of Allergy, Asthma, and Immunology