You go out to the local pizza parlor, order two slices with extra cheese, sit down at the booth with your pizza in one hand and coke in the other and chow down. A few hours later after you've arrived back home just in time to watch your favorite TV show, suddenly your stomach feels like it's about to erupt like a volcano. You run like a madman to the bathroom just in time to experience what seems to be the complete emptying of your insides.

Welcome to the world of food allergies and intolerances.

In the case of the runs after eating a couple of slices of pizza most likely you're lactose intolerant which is just one type of food allergy. Technically, you can be allergic to just about any kind of food but there are some that seem to be more common that others.

Before we go any further let's define exactly what a food allergy is. Food allergies can be broken down into 2 categories. The first one is hypersensitivity. This is an adverse reaction of the immune system itself and is unrelated to any actual physical effect of the food or food additive. These reactions are caused by immunoglobulin E (IgE) antibodies.

The second category is food intolerance. This is actually caused by the food itself and is not a function of the immune system itself overreacting to the food or food additive. The symptoms of an intolerance may be very similar to those of an actual immune symptom reaction but the causes are quite different.

Of the two, actual immune system reactions are the more common, though it does appear that a trend to intolerances, such as lactose intolerance, is on the rise. What actually happens with food allergies is that people with allergies produce IgE antibodies to specific epitopes in the food allergen. These antibodies bind to IgE receptors on the mast cells of tissue that are on the skin, digestive tract and respiratory system. The exposure of these antigens causes the release of histamines. This ultimately results in mucus secretion and muscle contraction which then leads to a wide range of symptoms which can range from unpleasant to serious or even severe. How severe?

Allergic reactions to food can be fatal almost immediately following the ingestion of food. Probably one of the most prevalent and dangerous of these food allergies are people who are allergic to peanuts. Just recently, as of this writing, a girl died simply from kissing someone who had recently eaten peanuts. That is how dangerous these allergies can be.

Less severe reactions to food allergies are oropharyngeal pruritus, angioedema, stridor, cough, dyspnea, wheezing, and dysphonia.

Aside from peanuts, the most common foods that people are allergic to are tree nuts, and shellfish.

Unfortunately the best way to avoid food allergies is to have a food allergy test done and then to avoid the foods that show positive on the test.