Adverse reactions to food can be categorised into IgE mediated reactions and non-IgE mediated reactions. Understanding the difference between the two is important as the approach to treatment is quite different. An IgE-mediated food reaction involves the immune system. The onset is sudden and includes vomiting, abdominal pain, urticaria and angio-edema. An IgE-mediated reaction to food can be diagnosed through a range of validated tests including skin prick testing.