Allergies are classified into Allergies mediated and non- Allergies mediated allergies. In Allergies mediated allergies the immune system produces exaggerated amounts of a distinct class of antibodies known as Allergies antibodies that are, specific for the particular offending allergens. These Allergies antibodies bind to the surface of cells in the body called mast cells which become 'Allergies -Sensitised' such that these cells can then identify particular allergens the next time they come in contact with the body. This process is called Sensitisation, and at this stage there are no physical symptoms of an allergy.
Mast cells are present in tissues that are in contact with the external environment, including the skin, nose, eyes, mouth, throat, stomach and gut. The next time that the same allergen is encountered the mast cells identify it as an intruder and produce histamine and other chemicals. It is the release of these chemicals from mast cells and their effects on the body that result in allergic symptoms.