WHAT IS AN ALLERGIC REACTION ?

Approximately 50 million Americans suffer from some form of allergic disease, and the incidence is increasing. When most of us think of allergies, we think of sneezing, a runny nose or watery eyes. While those are symptoms of some types of allergic disease, an allergic reaction is actually a product of several events occurring within your immune system.

  • The immune system

The immune system serves as the body’s defense mechanism against the countless different substances present in the air we breathe, the foods we eat, and the things we touch. Within this immense group of materials, the term “allergen” refers to any substance that can trigger an allergic response. Common allergens include pollen, mold, animal dander, and cockroach and house dust mite droppings.

Antibodies circulate in the bloodstream and are present in almost all bodily fluids. They help to capture unwanted invaders. People who have allergies have an antibody called Immunoglobulin E, or IgE . When allergens first enter the body of a person predisposed to allergies, a series of reactions occurs and allergen-specific IgE antibodies are produced. Following IgE production, these antibodies travel to cells called mast cells , which are particularly plentiful in the nose, eyes, lungs and gastrointestinal tract. The IgE antibodies attach themselves to the surface of the mast cells and wait for their particular allergen.

Each type of IgE has specific “radar” for one type of allergen only. That’s why some people are only allergic to cat dander (they only have the IgE antibodies specific to cat dander) and others seem to be allergic to everything (they have many more types of IgE antibodies.)

The next time an allergic individual comes into contact with the allergens to which he or she is sensitive, the allergens will be captured by the IgE. This initiates the release of chemical “mediators” such as histamine and other chemicals from the mast cells. These mediators produce the symptoms of an allergic reaction, such as swelling of tissues, sneezing, wheezing, coughing and other reactions.

The allergic reaction typically continues: these newly released mediators recruit other inflammatory cells to that site, resulting in additional inflammation. Many symptoms of chronic allergic disease—such as swelling, excessive mucus and hyperresponsiveness to irritating stimuli—are the result of tissue inflammation due to ongoing exposure to allergens.

It is not yet fully understood why some substances trigger allergies and others do not, nor why every person does not develop an allergic reaction after exposure to allergens. A family history of allergies is the single most important factor that predisposes a person to develop allergic disease. If one parent has allergic disease, the estimated risk of the child to develop allergies is 48%; the child’s risk grows to 70% if both parents have allergies.

  • Types of allergic disease

The existence of IgE antibodies is common to all forms of allergic disease. But the physical symptoms differ depending on the type of mediator released and where they act. When a person with allergies begins to experience symptoms, key questions are: What allergens am I reacting to? When, and how much, am I exposed to these substances?

Major allergic diseases include :

  1. allergic rhinitis, or “hay fever;”
  2. allergic conjunctivitis (an eye reaction);
  3. asthma;
  4. atopic dermatitis, or allergic skin reactions;
  5. urticaria, also known as hives;
  6. severe allergic reactions to substances such as food, latex, medications, and insect stings;
  7. and problems commonly resulting from allergic rhinitis—sinusitis and otitis media (ear infections).

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