Persistent urticaria caused by a common coloring agent.

As this case illustrates, foods or drugs may be ignored as possible causes of urticaria when they are not commonly accepted offenders or when they previously have been consumed with no adverse effect. In some instances, an additive or dye in a food or drug may be responsible for the reaction. In addition, a change of brands or dosage form of a drug may provoke urticaria or other reactions in sensitive individuals.