The Facts about Allergies

An allergy is a specific immunologic reaction to a normally harmless substance – a substance that does not bother most people. People who have allergies often are sensitive to more than one substance. Types of allergens that cause allergic reactions include pollens, dust particles, mold spores, food, latex rubber, insect venom and medicines.

But why are some people allergic to these substances while others are not?

Scientists think that people inherit a tendency to be allergic, although they probably do not have an inherited tendency to be allergic to any specific allergens. Children are much more likely to develop allergies if their parents have allergies, even if only one parent is allergic. Exposure to allergens at certain times when the body's defenses are lowered or weakened, such as after a viral infection or during pregnancy, seems to contribute to the development of allergies.

What is an allergic reaction?
Normally, the immune system functions as the body's defense against invading agents such as bacteria and viruses. In most allergic reactions, however, the immune system is responding to a false alarm. When an allergic person first comes into contact with an allergen, the immune system treats the allergen as an invader and mobilizes to attack. The immune system does this by generating large amounts of a type of antibody (a disease-fighting protein) called immunoglobin E, or IgE. Each IgE antibody is specific for one particular allergenic (allergy-producing) substance. In the case of pollen allergy, the antibody is specific for each type of pollen: one type of antibody may be produced to react against oak pollen and another against ragweed pollen, for example.

These IgE molecules are special because IgE is the only class of antibody that attaches tightly to the body's mast cells, which are tissue cells, and to basophils, which are blood cells. When the allergen next encounters its specific IgE, it attaches to the antibody like a key fitting into a lock, signaling the cell to which the IgE is attached to release (and in some cases to produce) powerful inflammatory chemicals like histamine, cytokines, and leukotrienes. These chemicals act on tissues in various parts of the body, such as the respiratory system, and cause the symptoms of allergy.

Some people with allergies also develop asthma. Symptoms of asthma include coughing, wheezing, and shortness of breath due to a narrowing of the bronchial passages (airways) in the lungs, and to excess mucus production and inflammation. Asthma can be disabling and sometimes can be fatal. If wheezing and shortness of breath accompany allergy symptoms, it is a signal that the bronchial tubes also have become involved, indicating the need for medical attention.

Information provided by the National Institute of Allergy and Infectious Diseases, National Institutes of Health.

Each year, Medical College of Wisconsin physicians care for more than 180,000 patients, representing nearly 500,000 patient visits. Medical College physicians practice at Children's Hospital of Wisconsin, Froedtert Memorial Lutheran Hospital, the Milwaukee VA Medical Center, and many other hospitals and clinics in Milwaukee and southeastern Wisconsin.