Wheat allergy is not very common but probably more common in children than in adults. A specific type of wheat allergy may cause life threatening symptoms when the affected person exercise after wheat ingestion.
Gluten hypersensitivity (coeliac disease) is not the same as wheat allergy. It is caused by gluten in wheat, rye and barley and for some also in oats. Coeliac disease is much more common than wheat allergy, and occurs in up to 2% of the European population.
Seed storage proteins (such as wheat gluten) and other proteins present in grain to protect it from attack by moulds and bacteria, have been found to be major allergens.