Figure 2. Suggested Schematic Treatment Protocol for Contact Immunotherapy for Alopecia Areata.

Treatment begins with application of 2% diphenylcyclopropenone to a 4 × 4-cm circular area on the scalp. After 2 weeks of sensitization, 0.001% diphenylcyclopropenone is applied to the scalp on a weekly basis, and the concentration of diphenylcyclopropenone is gradually increased until a mild eczematous reaction occurs. If a satisfactory hair regrowth is achieved, maintenance treatment may be used to reduce the recurrence rate. Contact immunotherapy with squaric acid dibutyl ester or other therapeutic agents can be considered when treatment failure or severe adverse effects occur.