Contact urticaria from cinnamic aldehyde.

Lip swelling developed following the use of a cinnamic aldehyde-containing mouthwash in a woman with allergic rhinitis and asthma. Open application of the mouthwash on the antecubital fossae of the patient and control subjects produced immediate erythematous or urticarial responses in all tested individuals. Subsequent investigation established cinnamic aldehyde as the responsible ingredient. The incidence of positive reactions was shown to depend on site of application, vehicle, concentration, and time of reading. Of several related cinnamates, only cinnamic acid produced easily detectable responses at similar concentrations.