A 29-year-old white man experienced a rather sudden onset of solar urticaria. The action spectrum ranged from about 250 nm to about 330 nm, but no wheal could be elicited in certain portions of his skin. The phenomenon was blocked by local injection of epinephrine and by arterial occlusion. A serum factor was demonstrated by passive and reverse passive transfer. Evans blue studies demonstrated that albumin from the serum entered the wheals as they formed. Histamine probably has no part in the production of this wheal as evidenced by the inability of locally-injected antihistamines or histamine depletion to alter the response. In addition, neither histamine nor kinin was detected in repeated dermal perfusion.
Sams WM, Epstein JH, Winkelmann RK. Solar UrticariaInvestigation of Pathogenetic Mechanisms. Arch Dermatol. 1969;99(4):390-397. doi:10.1001/archderm.1969.01610220018003