Allergic reactions occur when the immune system overreacts to a substance that should be harmless to the body. The immune system is made up of special cells, called white blood cells, which fight infection. An antigen is a protein that stimulates a reaction from the immune system. An allergen is a special type of antigen that should be harmless to the body; however, the immune system overreacts to the allergen, causing an allergic reaction.

When an allergen is present in the body, white blood cells recognize the allergen, and release chemicals into the bloodstream. These chemicals affect the skin, throat, lungs and intestines, causing the symptoms of an allergic reaction. A food allergy may occur after eating a very small amount of the food that causes the reaction.

The most common causes for food allergies include:

• Eggs
• Fish
• Milk
• Peanuts
• Shellfish
• Soy
• Sulfites
• Tree nuts
• Wheat