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.