Contact immunotherapy with diphenylcyclopropenone (DPCP) is presently considered the treatment of choice for extensive alopecia areata. However, a major concern with contact immunotherapy is that it causes various adverse effects (AEs) that contribute to discontinuation of treatment.We investigated whether a modified DPCP treatment protocol can promote hair regrowth with fewer AEs.All patients were sensitized with 0.1% DPCP and began treatment with 0.01% DPCP. Thereafter, the DPCP concentration was slowly increased according to the treatment response and AEs. This was a retrospective review of DPCP treatment with modified protocols in 159 patients with alopecia areata.Of the 159 patients, 46 (28.9%) showed a complete response and 59 (37.1%) showed a partial response. No patients had AEs after sensitization. During the treatment, only 3 patients (1.9%) showed severe AEs, and 55 showed moderate AEs; however, all were well controlled with antihistamines alone or antihistamines and medium-potency topical steroids. There was no association between treatment response and AEs.Sample size, subject composition, and the retrospective study design represent potential limitations.A modified DPCP treatment protocol with subclinical sensitization could induce a favorable therapeutic response and result in fewer AEs.