Allergies 101


An allergy occurs when the body’s immune system overreacts to any substance that is normally harmless. It is a hypersensitivity of the body that can produce reactions ranging from mild to life-threatening levels. Allergies can be caused by anything and tend to be genetically inherited. The gene responsible for certain cells of the immune system fails to distinguish between threatening and non-threatening substances. The American Academy of Allergy, Asthma and Immunology states that more than 50 million Americans suffer from some form of allergy.

How Allergies Occur

B-cells are a type of white blood cell in the immune system. They identify foreign particles and form antibodies that are designed to “attack” the particles. Antibodies are also called immunoglobulins. One of the types (IgE) is the immunoglobulin responsible for allergic reactions. When you come in contact with an allergen, a large quantity of IgE is produced, which attach to certain cells in the body that produce histamine. Histamine plays an important role in the body’s defense system but, if produced in large quantities as in an allergic reaction, can have negative effects of the body.


Allergies are classified into four different types. Type 1 hypersensitivities produce immediate responses within seconds of exposure. These can vary from a runny nose due to hay fever or an anaphylactic reaction from eating peanuts. Type 2 hypersensitivity produces reactions to “foreign” cells, such as if you receive a mismatched blood transfusion. Type 3 hypersensitivity results when allergens distribute throughout the whole body and a systemic inflammatory response occurs. Autoimmune disorders such as lupus or rheumatoid arthritis fall under Type 3 responses because the body fails to recognize its own cells. This type also includes drug allergies. Finally, Type 4 consists of delayed reactions that appear possibly days after an exposure. Contact dermatitis is an example of this type.

Common Allergies

Medline Plus, a service from the National Institutes of Health, lists the most common allergies as pollen, animal dander, bee stings, insect bites, medications, and certain plants and foods such as nuts, fish and shellfish. Some allergies, such as those caused by pollen and plants, are seasonal because they occur at a certain time of the year. Also a hypersensitivity may build, producing a reaction only on the second exposure. This means you might not have a problem eating a walnut the first time, but may experience a reaction the second time you eat it.


A mild allergic reaction can produce nasal congestion, a runny nose or red, itchy, watery eyes. Hives are intensely itchy wheals that typically appear on the chest and face but can be anywhere on the body. A moderate or severe reaction presents abdominal cramps, asthma-like wheezing, diarrhea, nausea, vomiting or weakness. Anaphylactic shock is the most extreme form of reaction–it can be fatal if not immediately treated. Anaphylaxis develops suddenly. The face, lips, tongue and airways start to swell, cutting off respiration. You may experience severe anxiety, tightness in the chest and difficulty breathing. Blood vessels begin to dilate, causing a severe drop in blood pressure, unconsciousness and shock.


Allergists and immunologists are doctors that help diagnose and treat allergies. Diagnostic tests include a “scratch” test or blood test to expose the person’s skin or blood to small amounts of allergen to determine the presence of a reaction. If your hypersensitivity to certain substances is identified, first and foremost you can ward off reactions by avoiding the allergens. For allergens that cannot be avoided, such as those in the environment, there are medications you can take. The only effective treatment for anaphylaxis is injecting adrenaline/epinephrine at the onset of symptoms. Another treatment, called immunotherapy, is available for people with severe allergies to substances that can’t be avoided or with allergic reactions that do not respond to medication.

About this Author

Based in Chicago, Jojo Genden is passionate about sharing her health and wellness expertise through writing since 2008. She holds a Bachelor of Science in biology from Rockford College, and a Bachelor of Science in nursing from Edinboro University of Pennsylvania. Genden is a registered nurse in the state of Illinois with a background in intensive care.