How Do Allergies Develop?

Exposure

An allergy is an inherited, hypersensitive immune system reaction to certain allergens, which are otherwise normal substances found in the environment, such as tree pollen, dust mites, animal dander, insect bites, some medications and proteins in certain foods. You do not inherit an allergy toward any particular allergen; instead, you inherit a tendency to develop allergies when exposed to allergens. Most allergies begin in childhood, but an allergy can develop at any time. You may grow out of one allergy only to develop another.

Response

Allergic reactions can cause a wide range of symptoms, including itching, coughing, sneezing, wheezing and hives (raised swellings under the skin) whenever you come in contact with the responsible allergen. Allergic reactions can also cause headaches or gastrointestinal distress. Hay fever, asthma, eczema and anaphylactic shock---a widespread response throughout the entire body, also known as anaphylaxis---are all allergic reactions that can result in mild to severe, and potentially deadly, reactions.

Antibodies

As soon as you inhale, touch or consume an allergen, your body's immune system begins to produce large amounts of antibodies in an attempt to fight off the offending substance. These antibodies, named Immunoglobulin E (IgE), are a type of protein produced by plasma and lymph cells in the skin, lungs and mucous membranes. Each type of IgE is specifically programmed to respond to a particular allergen. IgE antibodies attach themselves to the allergen and help the immune system destroy it. It is these warrior antibodies that actually cause allergic symptoms. Once antibodies to a specific allergen are formed, they will respond whenever you are exposed to that allergen.

Histamines

Other reactive chemicals released by body and blood cells at the onset of an allergic response include histamines. Histamines cause blood vessels to dilate and allow blood vessel walls to become more permeable. This, in turn, allows IgE and white blood cells to pass from the blood to the area affected by an allergen so they can begin the fight. When blood vessels dilate, blood pressure drops.

Progression

Allergic reactions become more serious when they progress. For instance, when the lining of your nose becomes irritated by an allergen, further symptoms of runny nose, nasal congestion and sneezing often follow. If your nose becomes inflamed, infection may set in.
Anaphylactic shock is a life-threatening allergic reaction, most often to insect stings, food allergens and drugs. The involvement of histamines causes a sudden drop in blood pressure, which is accompanied by swelling of tissue in the throat and tongue. The result is difficulty breathing and potential loss of consciousness.