Under normal conditions, your immune system is on guard against foreign invaders, known as antigens. These can be viruses, bacteria or any harmful substance. When an invader is found, the immune system releases protective proteins -- known as antibodies or immunoglobulins -- to attach to other immune cells called mast cells. When the offensive object encounters this mast cell/immunoglobulin hybrid, the antigen attaches to it. The mast cell then releases histamines and other chemicals to destroy the antigen. A food allergy -- or any allergy -- occurs when something triggers your immune system to have an abnormal response against a harmless substance that your body mistakes for a harmful agent.
True antigens prompt the response of one of four different types of immunoglobulin: G, M, A or D. Allergic reactions, however, prompt the production of a unique immunoglobulin, known as E, or IgE (immunoglobulin E). It's the presence of IgE that identifies a reaction as an allergic reaction. The half-life of IgE is 2.3 days, so if you have recurring symptoms over a period of days or weeks, it's due to continued exposure and continued manufacture of IgE [source: Ishizaka].
Common allergic symptoms include:
- skin rash
- runny nose
- watery eyes
Peanuts are the most likely food allergen to cause a life-threatening situation in the form of an anaphylactic reaction, which is basically a multisystemic meltdown that can put a person into a state of shock. For every five deaths related to a food allergy, four are caused by peanuts [source: Schwartz].
Food allergies aren't the only things that cause anaphylaxis. It can be triggered by penicillin, pollen and stings from insects such as bees or hornets. One treatment of anaphylaxis is a dose of epinephrine that helps end the state of shock by boosting blood pressure and opening up the airways in the lungs. Epinephrine can be administered (or self-administered) via injection into the thigh with a small penlike device that many food-allergic children and adults carry with them at all times.
Anaphylaxis can cause severe reactions to many parts of the body at once, including the throat, lungs and skin. However, anaphylactic reactions aren't always so severe, sometimes causing nothing more than a skin rash or mild asthma.
But it's possible to have allergylike symptoms and feelings after eating without any need to reach for the epinephrine pen. We'll learn how and why in the next section.