Idiopathic

This is the most common form of urticaria and particularly affects females with a peak incidence between 20 and 40 years of age. The onset is slow and eruptions tend to recur over periods of a few weeks, sometimes months. The majority show spontaneous remission within 6-8 months. Some however, may be prone to indefinite disease.

Some possible triggers include stress and viral infection (1)

Referene:

• (1) Powell RJ et al; British Society for Allergy and Clinical Immunology (BSACI). BSACI guidelines for the management of chronic urticaria and angio-oedema.Clin Exp Allergy. 2007 May;37(5):631-50.