Urticaria is actually a group of 12 separate conditions (see Table). The most common method to divide them is by their eliciting factors. The so called Spontaneous Urticarias are characterized by the fact that urticaria episodes occur seemingly “out of the blue”, i.e. there are no specific eliciting factors. The Spontaneous Urticarias are further subdivided by their duration into acute (lasting less than 6 weeks) and chronic (lasting longer than 6 weeks). The Physical Urticarias are all triggered by a physical stimulus, e.g. cold or pressure. The “Other Urticarias” group is made up of urticarias that are elicited by a specific factor, but where this stimulus is not a physical one.