Allergic response to a para-amino compound.

A 45-year-old woman reported recurrent episodes of urticaria, which had first appeared about one year earlier, when she started a diet which included eating frozen vegetable soup almost daily. Patch tests with the standard European series, food preservatives and colourings were performed and the results were only positive (+++, following the International Contact Dermatitis Research Group criteria) for p-ami-noazobenzene. After avoiding eating frozen vegetable soup from a coloured plastic wrapper, which was probably coloured with para-amino compounds that cross-reacted with p-aminoazobenzene, the patient's urticaria rapidly disappeared.