The exact cause to this is unknown.
Medically there has not been a reason found why a child or an adult may develop a certain food allergy.
What is known about the causes is that the immune system will attack certain properties in food.
Most often what is attacked is the proteins found in certain foods like shellfish, seafood, and peanuts.
The immune system is unable to break down the food that has been ingested, therefore it tries to get rid of the problem by creating allergens or an allergic reaction.
The causes are related to the antibodies found in foods.
The immune system doesn't recognize these antibodies and therefore the immune system tries to defend the body.
Think of the causes of food allergies like the causes of the flu or a cold.
You have bacteria that invades the body.
The body knows this is wrong so it will try to create some form block against the antibodies or bacteria.
As soon as the reaction is in place you experience an allergic reaction or allergy symptoms.
The allergy symptoms are a byproduct of the immune system trying to fight the foreign matter.
In other words it is a secondary cause to it.
The first reaction is the immune system releasing certain chemicals to help break down the food and flush the antibodies from the system.
The result of this is usually swelling, hives, diarrhea or constipation, and anaphylactic shock in patients that have severe cases of food allergies.
Overall it is the food that causes the allergic reaction.
When you cut the food from your diet you are saving your body from having to fight the foreign matter.
However, you can still develop other ones when you eat too much of one thing.
For instance if you ate rice every day for five years, and you were prone to it you could develop a food allergy to rice.
The immune system has just decided that you have too much protein or antibodies from the food and therefore it must fight it.
While the exact cause of food allergies is unknown, there have been significant studies to help individuals with food allergies handle the issues.
You will find that there is no cure for food allergies, just preventative methods.
It is important to understand how the immune system works to avoid further issue with any food allergy.