Allergies

Allergies or allergic reactions which are also referred to as hypersensitivity reactions are inappropriate immune responses to a normally harmless substance.  The immune system normally defends the body against foreign substances called antigens.  In susceptible people, the immune system over-reacts to certain antigens called allergens which are harmless to others.  When this happens, an allergic reaction is said to occur.

Some people are allergic to only one substance while others are allergic to many.  Allergen usually causes a reaction when they land on the skin or in the eye, are inhaled, eaten or injected.  It can also occur as part of a seasonal allergy or triggered by the intake of a certain drug or food or breathing in dust or animal dander.

In most allergic reactions, the immune system produces an antibody called Immunoglobin E when first exposed to the allergen.  This antibody then binds with basophiles in the bloodstream and mast cells in the tissues which are both types of white blood cells. The first exposure usually makes a person sensitive to the allergens with no obvious symptoms.  Subsequent encounters with the allergen causes the cells that have Immunoglobin E on their surface release substances that cause swelling or inflammation in the surrounding tissues.  This can cause further reactions to follow which will continually irritate and harm tissues.  Reactions range from mild to severe.