Food allergies are caused by the immune system reacting abnormally to the proteins present in certain foods and behaving as if they were microbes or foreign bodies. The immune response is to produce chemicals that kill microbes and this leads to allergic symptoms.
Normally, the immune system defends against microbial infection by producing specific proteins or antibodies that can identify and then "recognize" the proteins displayed on microbial cell walls. Once identified by the antibodies, the microbes are targeted by chemicals released during an immune response.
The antibody that most commonly misidentifies proteins in food as invasive agents is immunoglobulin E (IgE). It stimulates the release of several chemical immune mediators including histamine. Histamine leads to the swelling and dilation of the small blood vessels located in the face, lips, mouth, throat, airways and larynx, causing swelling or tightening of these areas. Histamine also induces an itching sensation as well as increasing mucus production in the mouth.
Food allergies usually run in families but may also be found in individuals with no family history of food allergies.
According to the United States Food and Drugs Administration, there are eight main types of food that trigger an allergic reaction. These include:
Certain fruits and vegetables including pears, apples, peaches, kiwi fruit, carrots, potatoes, parsnip, and celery can also trigger an allergic reaction as can commonly used food additives such as sulphite or benzoic acid.