Pathogenesis and classification of solar urticaria: a new concept.

Although its exact mechanism remains unknown, evidence supports the immunologic nature of solar urticaria. On the basis of experimental findings in the literature and our own observations, a new concept of the pathogenesis and classification of solar urticaria is presented. We propose two types of solar urticaria: type I, IgE-mediated hypersensitivity to specific photoallergens, which are generated only in patients with solar urticaria, and type II, induction of IgE-mediated hypersensitivity to a nonspecific photoallergen, which is generated both in patients with solar urticaria and in normal persons.