How to Identify Food Allergies

I am allergic to corn and its by-products. Here is a list of reactions I get when I eat corn:

As soon as the corn product touches my lips, I get a burning sensation, similar to the one we normally have when eating hot pepper. This reaction is immediate. The speed of this reaction has prevented me from ingesting corn products and having a much more severe reaction.

What happens next, if I decide to eat the product? My tongue, mouth and lips swell and lacerate. At this point it is wise for me to spit the food out. What is my usual 'more severe reaction' if I swallow? My esophagus gets raw. Then my small intestine inflames. The cramping begins, then severe pain and bloating, followed by diarrhea and purging. If I eat whole corn, the kernels pass through my entire digestive system in two hours, undigested. Yellow kernels are visible in the toilet. Everything that was in my system is forced out ahead of the corn, and I dehydrate.
I experience low blood sugar and depression.

This is considered a moderate reaction, non-life-threatening. I must inform medical practitioners, since many medications contain corn: Aspirin, dextrose, and many tablets manufactured by pharmaceutical companies.
If I need intravenous fluids and I receive dextrose made from corn, my veins and arteries become raw and I cease healing until the substance leaves my body.

How do you know if you have a food allergy?

This is the official list published by the Food and Drug Administration of the United States Government:

Hives
Flushed skin or rash
Tingling or itchy sensation in the mouth
Face, tongue, or lip swelling
Vomiting and/or diarrhea
Abdominal cramps
Coughing or wheezing
Dizziness and/or lightheadedness
Swelling of the throat and vocal cords
Difficulty breathing
Loss of consciousness

A very serious reaction is Anaphylaxis.
What is that? Swelling constricts the airways to the lungs making it difficult or impossible to breathe. Blood pressure drops and the body goes into shock. Death ensues.

So, it is best to see a physician if you have even moderate symptoms. Your physician will know what to do in your case. You may have to carry an epinephrine autoinjector (Epi-pen) to stop these life threatening symptoms. Your physician will teach you how to administer the medication properly.

Source: http://www.fda.gov/Food/ResourcesForYou/Consumers/ucm079311.htm