Urticaria is classified according to two different aspects. First and foremost, classification is according to the duration in acute (lasting less than 6 weeks) and chronic (lasting more than 6 weeks). The chronic form is further classified in chronic spontaneous urticaria and chronic inducible urticaria. Urticaria is always inducible when the wheals can be specifically triggered. In the case of a physical urticaria, the largest group of inducible urticaria, it can be induced by physical stimuli, such as, for instance heat, cold, light or pressure. The impact of this stimulant on the skin then leads to the appearance of wheals. In the case of contact urticaria, a further form of inducible urticaria, the contact of the skin with certain substances leads to the appearance of local wheals, for instance by touching stinging nettles or by coming into contact with a material you have an allergic reaction to. As the wheals are limited to the area of the skin which comes into contact with the stimulant, the distribution of the wheals is not incidental; they often form patterns which indicate the trigger. For instance in the case of solar urticaria, the wheals only appear on the light-exposed area while the areas not exposed to light and directly surround are absolutely free of symptoms. In the case of cholinergic urticaria, a frequent form of inducible urticaria, an increase in core body temperature triggers the development of wheals, whereby it is irrelevant whether the increase in body temperature was due to physical strain or, for instance, a hot bath. All inducible forms can also appear in combination with spontaneous urticaria.
Contrary to the inducible forms just brought forward, wheals develop “out of the blue” in the spontaneous form. The skin lesions appear beyond the control of the patient and on all possible areas of the skin, the borders of the hives are purely coincidental. Stress and heat may favour the development however, they are not really necessary for the symptoms to appear. The clearly most frequent form is acute spontaneous urticaria. About one in four people is affected at some time during life. Luckily the symptoms disappear again in the vast majority of cases in a few days or weeks. It is generally termed acute urticaria. If the symptoms last longer than 6 weeks it is termed chronic urticaria. This urticaria can last for several months or years (sometimes decades). This fact alone justifies the high number of patients
The majority of the patients suffering from chronic urticaria suffer from chronic spontaneous urticaria. The inducible forms of urticaria are less frequent. In this group most of the patients suffer from symptomatic dermographism (also urticaria factitia) or from cold urticaria. Aquagenic urticaria (triggered by water) or vibration-induced angioedema are absolute “rarities”. All the forms of urticaria are listed in the following table according to their classification.
|Acute, spontaneous urticaria|
|Chronic spontaneous urticaria |
|Chronic inducible urticaria|
|Spontaneous appearance of wheals, angioedema or both for less than 6 weeks for known and unknown causes||Spontaneous appearance of wheals, angioedema or both for more than 6 weeks for known and unknown causes|
Contact urticaria (frequent)
Aquagenic urticaria (very rare)
1also called urticaria factitia or demographic urticaria,