Allergic contact dermatitis to dyclonine hydrochloride simulating extensive herpes simplex labialis

Two patients developed allergic contact dermatitis to 1% dyclonine hydrochloride gel, a nonprescription topical anesthetic widely marketed for the symptomatic treatment of herpes simplex labialis. Both patients mistakenly believed that the eruption was expanding herpes simplex labialis, which resulted in their more frequent application of the dyclonine hydrochloride and a delay in diagnosis. Dermatologists should recognize that 1% dyclonine hydrochloride gel can cause allergic contact dermatitis that can masquerade as widespread herpes simplex labialis.