Food hypersensitivity refers to all types of overreactions that an organism can have against a food component. Food sensitivity includes food allergy and food intolerance.

Food allergy is a specific form of food hypersensitivity that activates the immune system, leading to an exaggerated response. An immunological reaction is a reaction against foreign substances entering the body. An allergen (nearly always a protein in the offending food) sets off a chain of reactions in the immune system including the release of antibodies. These antibodies trigger the release of body chemicals, such as histamine, which give rise to various symptoms such as itchy skin, a runny nose, coughing or wheezing.

Common food allergens are cow's milk, soy, eggs, fruits, peanuts, treenuts such as hazelnuts, seafood and most recently allergies to products that have not been traditionally used in Europe such as kiwi or mango.

Already a small amount of food proteins can trigger an allergic reaction. The immune system protects our body from harmful foreign proteins (i.e. antigens) by generating a response to eliminate them. In a true allergic reaction, the immune system produces antibodies. An antibody is a protein that specifically binds with an antigen to inactivate it and remove it from the body. The class of antibodies known as immunoglobulin E (Ig E) reacts with the antigen and this in turn triggers a reaction with the mast cells (tissue cells) and basophiles (a type of blood cell). Mast cells are found below the surface of the skin and in the membranes lining the nose, respiratory tract, eyes and intestine. A substance called histamine or other substances such as leukotrienes and prostaglandins are released from mast cells and they cause allergic responses. These adverse reactions are immediate and usually localised.

Fortunately, most allergic reactions to food are relatively mild, but a small number of people have a very severe and life-threatening reaction, called anaphylactic shock. An anaphylactic shock is a sudden drop in blood pressure that can be fatal if not treated quickly. It can sometimes occur within a few minutes of exposure. Peanuts are well known for causing anaphylactic shock and emergency treatment includes the use of an injection of adrenaline to open airways and to constrict blood vessels.

Some allergic reactions take several hours or even days to develop. These are called delayed hypersensitivity reactions; typical symptoms involve the skin, lungs and intestines.

Food intolerance is an adverse reaction to a food that does not involve the immune system. The reaction is due to non-digestion/non-absorption of a specific food or component. The symptoms are specific to individuals. Examples are lactose intolerance and fructose intolerance.

Presently, no adequate treatment exists to cure food intolerances. Once diagnosed, the only effective treatment is to avoid the foods that cause problems. Only for lactose intolerance enzyme preparations with the lactase enzyme are available in some countries.

Types of Food Allergies and Intolerances:

It should be noted that in some cases the same product can cause both allergies as well as an intolerance :

Milk : allergy against the proteins in milk, intolerance against the lactose

Wheat : allergy against the wheat proteins, intolerance against gluten (celiac disease)