Patients with chronic urticaria undertake a five week elimination diet (pseudoallergen free diet). The efficacy of the diet will be determined by symptom score, by the use of rescue medication (oral antihistamines and glucocorticosteroids) and by a Quality of Life Questionnaire on week 0 and week 5. All patients with sufficient response (regarding the urticaria score) enter a second dietary part over six weeks, whereas a provocation diet is carried out. Each diet week a choice of pseudoallergen rich food is added, sorted by the type of pseudoallergens (e.g. biogenic amines, organic acids, flavours, additives). This study is conducted to investigate if the provocation diet could be a new diagnostic intervention to elucidate clinical relevant pseudoallergens.