Solar urticaria without inhibitory spectrum: demonstration of both circulating photoallergen and reaginic antibodies.

An 18-year-old man with solar urticaria is described. The action spectrum ranged from 400 to 500 nm. No inhibition spectrum was found, i.e., the wheal that is induced by visible light was not inhibited by immediate pre- or postirradiation of test sites with light waves longer than 620 nm. The patient developed a wheal at the site of injection of his own serum that had previously been exposed to light in vitro. Though the ordinary passive transfer reaction yielded a positive result, a passive transfer study with the patient's serum preheated at 56 degrees C for 2 h showed a negative result. These data suggest that he had both circulating photoallergen and reaginic antibodies.