Contact urticaria refers to a wheal-and-flare response occurring on the application of chemicals to intact skin.
Standard closed patch tests read at 48 hours after application yield misleading information; observations should be made instead using open patch tests 15 to 30 minutes after application.
There are three major subdivisions of the syndrome: nonimmunologic cause (such as application of histamine), immunologic cause (immediate hypersensitivity), and uncertain cause (such as application of ammonium persulfate). Our patient had contact urticaria due to the insect repellent, diethyltoluamide. The experimental data suggest that this case was due to an immunologic response (immediate hypersensitivity) and demarcates the specificity of response.
The immunologically mediated cases cover a broad spectrum of manifestations from contact urticaria only to local urticaria plus asthma and, in extreme sensitivity, includes anaphylactoid responses.
Maibach HI, Johnson HL. Contact Urticaria SyndromeContact Urticaria to Diethyltoluamide (Immediate-Type Hypersensitivity). Arch Dermatol. 1975;111(6):726-730. doi:10.1001/archderm.1975.01630180054004