What is a Food Allergy (Hypersensitivity)?

A food allergy or hypersensitivity is an abnormal response to a food by our immune system. As illustrated in Figure, this non-toxic allergic hypersensitivity is immune mediated, i.e. immunological mechanism is involved or suspected.

To understand this mechanism, we need to refresh our understanding of the immune system Antibodies, we learnt, are immunoglobulin produced by plasma cells in response to an antigen or allergen. Antigen, you may already be aware, is usually a foreign substance (i.e. protein, bacteria, virus, polysaccharide etc.) that stimulates antibody production. Allergens, on the other hand, are substances foreign to the body that on interaction with the immune system causes an allergic reaction. Five classes of antibodies have been identified. Immunoglobin A (IgA), Immunoglobin D (IgD), Immunoglobin E (IgE), Immunoglobin G (IgG) and Immunoglobin M (IgM).