Food Allergy

Updated: May 2003

Article Summary

Food allergy is an immune system reaction to food. The chemicals released by the immune system cause a variety of symptoms. Antibodies are the component of the immune system that initiates the reaction. IgE antibodies cause immediate food allergy reaction. Non-IgE antibodies likely cause delayed allergic reactions.

What is Food Allergy?

Food allergy is an immune system response to a specific food. The immune system thinks the food is harmful and launches an attack when that food enters the body. The symptoms experienced during an allergic reaction are caused by this immune system response.

The purpose of the immune system is to kill harmful substances, such as germs, that enter our body. The immune system is like an army that protects our body from outside invaders. During an immune system attack, chemicals are released to kill harmful germs. In addition to killing the germs, the chemicals also make us feel sick. Someone with a cold usually has a runny nose, fever and watery eyes. These symptoms are caused by the chemicals the immune system released to kill the cold virus. Histamine is one of the chemicals in the immune system’s arsenal. Anti-histamine medication is a component of most cold medications. Anti-histamine medication blocks the effect of histamine and prevents many of the symptoms associated with a cold.

An allergy happens when your immune system thinks that an ordinary substance is harmful. The immune system releases chemicals just as it would if you had a harmful germ in your body. Many triggers can cause an allergic reaction. An allergen is a substance that can cause an allergy. Cat dander, dust mite, ragweed pollen and foods are common allergens. Some people have a runny nose and watery eyes when they are around cats. They may feel like they have a cold. Their immune system is releasing chemicals to fight the cat dander. Similar chemicals are released when the immune system is fighting harmful germs or an allergen.

In summary, food allergy is an immune system reaction to food. The chemicals released by the immune system cause a variety of symptoms.

What happens in the body to cause an allergic reaction?

Antibodies are compounds in our blood that activate an immune system reaction. Antibodies are also called immunoglobulins (abbreviated as “Ig”). In the previous paragraph, the immune system was described as an army. The antibodies would be the soldiers that initiate an attack on the enemy. There are several types of antibodies that cause allergies. These antibodies can be classified as IgE antibodies or non-IgE antibodies.

IgE Antibodies

In susceptible people, the first encounter with the food causes the body to make IgE antibodies toward that food.  IgE antibodies are specific and individual. One person may have IgE antibodies to milk and wheat. Another person may have IgE antibodies to egg and peanut. If a person has developed IgE antibodies to a particular food, they are “sensitized” to that food.

The IgE antibodies attach to mast cells. Mast cells are found in the digestive and respiratory system and the skin. Mast cells are tiny balloons filled with the immune system chemicals.

When a sensitized person consumes the offending food, an allergic reaction may happen. If the offending food can interact with the IgE antibody, the mast cells will burst. The chemicals stored in the mast cells will be released into the body. These chemicals cause the allergy symptoms.

IgE antibodies cause immediate food allergy reactions. In other words, the symptoms are felt very quickly after the offending food (allergen) is consumed. Some of the symptoms caused by IgE antibody reactions are:

The following story is meant to illustrate the IgE antibody reaction using our “army” analogy.

The “IgE soldiers” have been notified that an enemy (“Egg”) has entered the body. Some of the “IgE soldiers” get ready to fight “Egg”. These soldiers march over to the “Mast Cell Chemical Storage Units”, and wait for “Egg”. A little while later, “Egg” gains access to the body and grabs the “IgE soldiers”. This causes the “Mast Cells” to burst open. Many chemicals are released in an attempt to destroy “Egg”.

This story illustrates that the interaction of the offending food and the food specific IgE cause the mast cells to burst. The chemicals released from the mast cells cause the allergy symptoms.

Non-IgE Antibodies

IgM, IgG and IgA food specific antibodies have been detected in people’s blood. The process by which these antibodies cause an allergic reaction is complex and is not well understood. These antibodies likely cause delayed allergic symptoms.

Celiac disease is an autoimmune disorder. This means that the immune system produces antibodies that attack its own body tissues (autoantibodies). The antibodies are IgG or IgA. Autoantibodies cause inflammation and destruction of body tissues. In celiac disease, autoantibody production is triggered by the consumption of gluten (wheat, rye and barley).