Spontaneous urticaria is the most common form of urticaria. One out of four people will present spontaneous urticaria over the course of their lives. The key characteristic is that the symptoms occur "out of the blue." In general, the signs of illness (wheals, itchiness and angioedema [subcutaneous swelling]) cannot be reproduced on command, and hence one examination is not enough to determine the trigger and causes behind the occurrence.
Spontaneous urticaria generally lasts only a few days or weeks. It is then described as acute spontaneous urticaria or simply acute urticaria. For up to 10% of all patients with a spontaneous acute urticaria, the symptoms last longer than 6 weeks. One then speaks of a spontaneous chronic urticaria, or simply chronic urticaria.