An allergy is an overreaction of the body’s defence system (the immune system) to one or more substances such as food proteins or pollens that are normally innocuous to most people. These substances are known as allergens.
In people with an allergy, the immune system treats these allergens as intruders and attacks them, resulting in the production of antibodies called Immunoglobulin E (IgE). These antibodies bind to specialised cells (mast cells and basophils) that release substances into the body to defend against the allergen causing an immediate allergic reaction.
This reaction usually causes symptoms in the nose, eyes, lungs, throat, sinuses, ears, cardiovascular system, skin or the stomach. A subsequent exposure to that same substance will elicit this allergic response again.