Four cases of recurrent pseudo-scarlet fever caused by phenathrene alkaloids with a 6-hydroxy group (codeine and morphine).

Four patients with a clinical picture resembling that of scarlatina are described. This clinical picture was found to be based on a delayed-type allergy for codeine and morphine. Investigation showed that the codeine or morphine allergy is essentially dependent on the hydroxyl group at the 6 position of the basic phenanthrene structure but only when this group is bound equatorially, as is the case for codeine and morphine.