Patch test sensitization to D & C yellow No. 11 and simultaneous reaction to quinoline yellow

The quinoline color D & C Yellow No. 11 was added to a standard test series. Of 88 patients tested with 1% in PEG, four showed unexplained positive test reactions. One patient had a "flare-up" reaction after 14 days. At rechallenge he reacted to a dilution down to 0.00001%. Simultaneous reaction with the chemically related commonly used food color Quinoline Yellow (E 104) suggests cross-sensitivity.