A food allergy is any adverse reaction to a food or food component involving the body's immune system . Some adverse reactions to foods do not involve the immune system and are known as food intolerance , e.g. food poisoning or the inability to properly digest certain food components such as lactose or gliadin .

A true allergic reaction to a food involves two primary components:

1. Contact with food allergens (part of the food that stimulates the immune system);
2. Immunoglobulin E ( IgE : an antibody in the immune system that reacts with allergens ) and mast cells (tissue cells) as well as basophils (blood cells), which release histamine or other substances causing allergic symptoms when IgE antibodies attach onto these cells.

Although most Americans consume a wide variety of food additives daily, only a small number have been associated with reactions. These reactions do not involve the immune system and therefore are examples of food intolerance rather than food allergy.

While most allergic reactions to food are relatively mild, a small percentage of food-allergic individuals have severe reactions that can be life-threatening. Anaphylaxis is a rare but potentially fatal condition in which several different parts of the body experience food-allergic reactions simultaneously, causing hives , swelling of the throat and difficulty in breathing.

Food allergies can cause a host of symptoms , including : swelling of the lips; tongue or throat; hoarseness; cough; hives ; skin rashes ; a runny nose and watering eyes; and asthma . Sometimes symptoms are limited to nausea, vomiting, or cramping diarrhea. Symptoms of a food allergy are highly individualistic and usually begin within minutes to a few hours after having eaten the offending food.

The most common food allergens involved in food allergy are shellfish, milk , fish, soy, wheat , peanuts , egg and tree nuts such as walnuts. Pharmacologically active substances found in food include histamine , tyramine, tryptamine and serotonin , which may be consumed in foods such as red wine, cheese, yeast extract, avocados and bananas. In susceptible people, these foods can trigger urticaria , facial flushing and headaches. Patients with hypersensitivity to avocados, bananas, kiwis or chestnuts sometimes exhibit clinical reactions to latex . This is termed Cross-Reactivity .

There are a variety of forms in which a food hypersensitivity expresses itself. These include:

• Oral Allergy Syndrome
• Food Intolerance
• Gastointestinal disease with an immunologic basis, e.g. Chronic Ulcerative Colon ; Celiac Disease ; Crohn Disease .