Diphencyprone, formerly known as DPCP and Diphenylcyclopropenone, is a topically administered drug intended for treating alopecia areata and alopecia totalis. Topical immunotherapy using diphenylcyclopropenone may also be an effective treatment option for recalcitrant warts. Diphenylcyclopropenone acts as a local irritant, triggering a local sensitization. It triggers an immune response that opposes the action of the autoreactive cells that otherwise cause hair loss.