Histamine is a biologically active component that can be found in many foods and beverages. Intake of excessive histamine from foods or beverages, can trigger symptoms including urticaria. A low histamine diet has been recommended as one of the possible treatments for patients with chronic urticaria. There are very few studies to confirm the effectiveness of such diets and, to the investigators' knowledge, none from Asia where high histamine containing meals are often eaten (personal observations). The objective of the present study is to investigate the therapeutic effect of low histamine diet in relieving symptoms in patients with chronic urticaria with or without angioedema, and / or pruritus (U/A/P). The investigators hypothesize that following a low histamine diet for 4 weeks, the symptoms of patients with chronic U/A/P should improve.