**2. Definition**

Urticaria is a relatively common condition that can persist for weeks, months or years and can affect significantly quality of life [1]. It is a heterogenous skin disorder that can be acute or chronic, intermittent or persistent and can occur alone or in association with other related conditions. The aetiology is often difficult to determine particularly in chronic urticaria1 .

Urticaria is characterised by the development of wheals, angioedema or both on the skin [2]. It is characterised by 3 features [3]:


Angioedema [3] is characterised by sudden onset localised swelling of submucosal surfaces of the upper respiratory and gastrointestinal tract, deeper dermal layers of skin including subcutaneous tissue [4]. It is associated more with pain and burning rather than itching and generally takes longer – up to 72 hours - to resolve [3].

Wheals can occur in combination with angioedema in 40% and angioedema can be the only manifestation of urticaria in 20% of patients [1, 5].

Urticaria are classified into 2 major categories [2, 3, 5] – acute vs. chronic – according to duration, and - spontaneous vs. inducible - according to aetiology [5]. Acute urticaria resolves in less than 6 weeks. Chronic urticaria lasts for longer than 6 weeks (**Table 1**).

Many cases of acute urticaria (AU) resolve but 20–45% continue and become chronic [5]. The most common causes for acute urticaria include acute viral infections and allergic reactions to food, medication, latex and insect bites [5, 6].

Chronic urticaria (CU) are clinically subdivided into spontaneous (CSU) - no specific eliciting factor(s) can be identified [7] - and inducible (CINDU) when specific identifiable stimuli trigger urticaria [7].

In summary CSU is characterised by spontaneous occurrence of wheals and or angioedema for 6 or more weeks, resulting from unidentified causes and pathophysiology that is not completely understood [3]. While autoimmune disease (21%), chronic infection (29%), and immune dysfunction (4%) may become evident over

time, in 45% of CSU cases no underlying cause can be found even after 10-year follow-up [4, 5, 8]. In these cases, anaphylaxis does not occur even if angioedema may be present [1, 4].

It is worth mentioning that the term CSU replaced the terms chronic idiopathic urticaria and chronic autoimmune urticaria, whereas the term CINDU replaced the terms physical urticaria and other forms of inducible urticaria, such as cholinergic and aquagenic urticaria [6].

Two or more different subtypes of urticaria may coexist in any given patient. There is often overlap between CSU and CINDU [3, 5].
