Food allergies occur when the immune system mounts an attack on certain proteins in certain foods. The substances in the food that trigger this immune-system response are called allergens.
The immune system is a complex network of cells and molecules that help defend the body against foreign substances. When a properly functioning immune system detects a foreign substance, it responds to this threat by producing proteins called antibodies against the invaders. The antibodies will recognize and attack this foreign substance when they next encounter it. This "battle" is what causes the allergy symptoms.
In food allergy:
The immune system mistakenly sees a harmless substance in the food as harmful, and churns out antibodies-known as immunoglobulin E (IgE) - to attack it.
These antibodies will circulate in the blood, attached to special cells called mast cells, which are part of the immune system. This occurs in order to protect against future invasion by that substance.
The next time a person eats that food, the substance to which he is allergic (the allergen) enters the body, and attaches to the IgE on mast cells.
The mast cells respond by releasing a host of powerful chemicals, including histamine, to 'protect' the body. This produces allergic symptoms.
Histamine contributes to inflammation and causes symptoms such as swelling on the skin and itching. It is responsible for the hives, or welts, that appear on the skin when a doctor tests for allergy. These hives show the presence of IgE and are one of the best indications of allergy.
Nice To Know:
Allergic symptoms can start within minutes or an hour or two after eating the food. In people who are extremely allergic to a food, merely inhaling miniscule amounts of the food or touching the food is enough to trigger a reaction. However merely touching the food rarely causes a systemic reaction. In fact, it is often quite surprising that a peanut allergic individual may get peanut butter on her skin without having a systemic reaction.