Urticarial reactions to the sun's rays, though uncommon, present a disturbing and, at times, incapacitating disorder. A variety of mechanisms and disease relationships have been reported, including the presence of exogenous and endogenous photosensitizers, endocrine and hepatic disorders, and infectious states.
The syndrome "solar urticaria" specifically describes an immediate urticarial response to light energy in which no photosensitizer or associated disease process can be detected and which, in certain instances appears to be an immediate allergic reaction. In solar urticaria, within a few minutes of minimal actinic exposure, erythema and pruritis occur and are soon followed by a wheal surrounded by an irregular flare but no pseudopod formation. The lesion generally develops as a single wheal involving the light-exposed area.
Epstein, Vandenberg, and Wright,1 writing in the August issue of the Archives of Dermatology, described a multiple-wheal variety of solar urticaria with pseudopod formation due to visible light rays.
SOLAR URTICARIA. JAMA. 1963;185(9):723-724. doi:10.1001/jama.1963.03060090055020