Cross-reactions among parabens, para-phenylenediamine, and benzocaine: A retrospective analysis of patch testing

Background: Parabens are alkyl ester derivatives of parahydroxybenzoic acid and are the most commonly used preservatives in the cosmetic industry. Cross-reactions with para-amino compounds, namely, benzocaine and para-phenylenediamine (PPD), have been reported but are thought to be extremely rare. Objective: To evaluate the rate of cross-reactivity between parabens, PPD, and benzocaine in a population of patients patch-tested in a hospital-based contact dermatitis clinic. Methods: A retrospective analysis of 4,368 patients consecutively patch-tested between July 1989 and June 2005. Results: Our study demonstrated that the rate of cross-reactions to parabens in PPD- and benzocaine-positive patients combined is 2%. Conclusion: This cross-reaction rate is significant in the tested population but still falls within the previously reported rates of sensitivity to parabens in the general population (0 to 3.5%).