So What is it?

...a food hypersensitivity?

A food hypersensitivity is a bad reaction to a food that is otherwise perfectly safe to eat.

...a food allergy?

A food allergy is an abnormal, exaggerated reaction of the immune system to certain foods. It involves the production of a specific kind of antibody which reacts to a particular food component and, in doing so, causes an allergic reaction.

...a food intolerance?

A food disease is also a bad reaction to some food ingredient. However, the immune system is not involved. Examples include lactose intolerance due to the absence of the enzyme lactase and migraine induced by red wine.

...coeliac disease?

Coeliac disease is an example of an “auto immune” disease in which the body is attacked by its own immune system. The reaction is triggered by eating gluten-containing foods. Gluten is a mixture of proteins called prolamins and glutenins that are found in cereals such as wheat, barley, rye and oats.

...an allergen?

An allergen is any normally harmless substance that causes an immediate allergic reaction in a susceptible person. Food allergens are almost always proteins although other food constituents, such as certain additives, are known to have allergenic (allergy-causing) properties.

...cross-reactivity?

Cross-reactivity can happen when one protein is similar to another protein that is an allergen. The proteins don’t have to be in the same food. Some people have a latex allergy which can be associated with a number of food allergies including banana, avocado, chestnut, apple, carrot, celery, papaya, kiwi, potato, tomato and melons. Allergy to tree pollen can also be associated with allergies to fruit. For instance people who are allergic to birch pollen are also allergic to apples, almonds, peaches, kiwi, carrots, celery, peppers and hazelnut. Cross-reactivity with melons, tomatoes and oranges has been recorded in people who are allergic to grass pollen.