Diagnosis and classification of urticaria Urticaria is per definition the appearance of wheals and/or angioedema. However, as described in the following, there are many other diseases presenting with wheals and angioedema that are not chronic urticaria, e.g. allergic anaphylaxis. Wheals are characterized by three features: (1) swelling and erythema, (2) itching/burning sensation and (3) transient nature with the skin returning to normal within 1-24 hours. According to the European Academy of Allergy and Clinical immunology (EAACI), the Global Allergy and Asthma European Network (GA 2 LEN), the European Dermatology Forum (EDF) and the World Allergy Organization (WAO) guidelines [Zuberbier et al. 2014], which are the internationally accepted guidelines, urticaria can be classified according to duration and cause. Acute urticaria is defined as the occurrence of spontaneous wheals with or without angioedema for less than 6 weeks, whereas chronic urticaria is occurrence of hives with or without angioedema for 6 weeks or more. Chronic urticaria is classified according to whether it is inducible or not into chronic spontaneous urticaria or chronic inducible urticaria. Chronic spontaneous urticaria may be due to known (e.g. autoantibodies) or unknown causes. The inducible urticarias include cold urticaria, delayed pressure urticaria, solar urticaria, heat urticaria, vibratory urticaria, cholinergic urticaria, contact urticaria, and aquagenic urticaria. A patient may well have more than one type of urticaria. Most of the conditions mentioned are mainly mediated by histamine (Table 1). Wheals and angioedema are not always urticaria Type I allergies should be suspected from a thorough history that reveals consistent appearance of wheals or angioedema after ingestion/