What is an allergic reaction?

Allergies often bring to mind sneezing, runny nose or watery eyes. While these are symptoms of some types of allergic disease, an allergic reaction is actually a result of a chain reaction that begins in your genes and is expressed by your immune system.

What is happening inside your body when you have an allergic reaction? Read on to find out.

The Immune System

Your immune system controls how your body defends itself. For instance, if you have an allergy to pollen, your immune system identifies pollen as an invader or allergen. Your immune system overreacts by producing antibodies called Immunoglobulin E (IgE). These antibodies travel to cells that release chemicals, causing an allergic reaction. This reaction usually causes symptoms in the nose, lungs, throat, sinuses, ears, lining of the stomach or on the skin.

Each type of IgE has specific "radar" for each type of allergen. That's why some people are only allergic to cat dander (they only have the IgE antibodies specific to cat dander); while others have allergic reactions to multiple allergens because they have many more types of IgE antibodies.

It is not yet fully understood why some substances trigger allergies and others do not, nor why some people have allergic reactions while others do not. A family history of allergies is the single most important factor that puts you at risk of developing allergic disease.

Types of Allergic Disease

Approximately 50 million Americans suffer from some form of allergic disease, and the number is increasing. There are several types of allergic disease, which you can learn more about by reading the other Tips brochures in this series.

Allergic rhinitis may be seasonal or year-round. The seasonal allergy, often called "hay fever," typically occurs in the spring, summer or fall. Symptoms include sneezing, stuffy or runny nose and itching in the nose, eyes or on the roof of the mouth. When the symptoms are year-round, they may be caused by exposure to indoor allergens such as dust mites, indoor molds or pets.

Allergic conjunctivitis occurs when the eyes react to allergens with symptoms of reddening, itching and swelling. Atopic dermatitis, or eczema, often results from allergen exposure to your skin. Symptoms include itching, reddening and flaking or peeling of the skin. Symptoms begin in childhood for 80% of those with atopic dermatitis. Over 50% of those with atopic dermatitis also develop asthma.

Urticaria, or hives, is characterized by itchy red bumps that can occur in clumps and be either large or small. Hives are often triggered by certain foods or medications.

Asthma is a chronic lung disease characterized by coughing, chest tightness, shortness of breath and wheezing. Up to 78% of those with asthma also have allergic rhinitis. The role of allergy in asthma is greater in children than in adults.

When you experience asthma symptoms, your inflamed airways become narrowed, making it more difficult to breathe. If you have allergies, inhaling allergens may cause increased swelling of your airway lining and further narrowing of your air passages. Asthma may also occur as a result of respiratory tract infections or exposure to irritants like tobacco smoke.

People with food allergies may have severe and possibly life-threatening reactions if they eat those foods. The most common triggers are the proteins in cow's milk, eggs, peanuts, wheat, soy, fish, shellfish and tree nuts.

Food, medications, insect stings and exposure to latex can trigger anaphylaxis. Anaphylaxis (pronounced an-a-fi-LAK-sis) is a serious allergic reaction that comes on quickly, causing mild to severe symptoms that affect various parts of the body.

Symptoms of anaphylaxis include a feeling of warmth, flushing, tingling in the mouth or a red, itchy rash. Other symptoms may include feelings of light-headedness, shortness of breath, throat tightness, anxiety, pain/cramps and/or vomiting and diarrhea. In severe cases, you may experience a drop in blood pressure that results in a loss of consciousness and shock. Without immediate treatment with an injection of epinephrine (adrenalin), anaphylaxis may be fatal.

Sinusitis and otitis media are other common allergic diseases often triggered by allergic rhinitis. Sinusitis is a swelling of the sinuses, which are hollow cavities within the cheek bones around your eyes and behind your nose. Otitis media-or ear infections-is the most common childhood disease requiring physician care. If not properly treated, it can affect a child's speech and language development.

Diagnosing and Treating Allergic Reactions

An allergist/immunologist, often referred to as an allergist, is best qualified to treat allergic diseases. To determine if you have an allergy, your allergist will take a thorough medical history and do a physical exam. He or she may perform allergy skin testing, or sometimes blood testing, to determine which substance is causing your allergy.

Once your allergy triggers are identified, your allergist can help you establish a treatment plan that is right for you. Allergy shots, or immunotherapy, may also be recommended. See the Allergy Shots brochure in this series for more information.

While there is not yet a cure for allergic disease, your allergist can properly diagnose the problem and develop a treatment plan to help you feel better and live better.

Healthy Tips

• Allergy symptoms are the result of a chain reaction that starts in your immune system.
• If you have a family history of allergies, you are at a much higher risk of developing allergic disease.
• The types of allergic disease include allergic rhinitis (hay fever), eczema, hives, asthma and food allergy.
• Food, medications, insect stings and exposure to latex can trigger anaphylaxis, which is a serious allergic reaction that happens very quickly and in some instances may be fatal.
• If you (or anyone you are with) begin to have an allergic reaction, call for medical help to get to the closest emergency room.
• Talk to your allergist about the many treatments available to help you feel better.