Objective：There is no useful standard for assessing the therapeutic efficacy of treatments for scalp psoriasis. We investigated whether the combination of an improvement of ≥90% on the Psoriasis Scalp Severity Index (PSSI90 achievement), objectively evaluated by a physician, and reduction in scalp itch, subjectively evaluated by the patient, can be used as a new standard for assessing the therapeutic efficacy of scalp psoriasis treatments. Methods：In a survey (766 patients) of the current status of topical treatments for scalp psoriasis, we compared PSSI90 achievers to PSSI90 non-achievers in a 299-patient subgroup treated with a fixed combination of calcipotriol plus betamethasone dipropionate (Cal/BDP gel). The subgroup was large enough to perform an analysis to determine whether the combination of PSSI90 achievement and reduction in scalp itch can be used as a standard of therapeutic efficacy. Results：In the Cal/BDP gel monotherapy group, the longer Cal/BDP gel was used, the higher the proportion of patients achieving PSSI90, reaching 30.6% after 3 months. The PSSI90 achievers also showed higher satisfaction with and stronger preference for Cal/BDP gel. In this group, scalp itch was significantly reduced 1 month after treatment initiation with Cal/BDP gel and continued to decline over time. However, an analysis of the relationship between the rate of change in the PSSI score and in the itch score revealed that 11.3% of patients experienced increasing itchiness despite an improvement in PSSI score at 3 months. This suggests that intractable cases exist where the itch gets worse despite an improvement in skin symptoms. Conclusions：In the treatment of scalp psoriasis, evaluation of the therapeutic efficacy based only on “PSSI90 achievement” runs the risk of missing cases with worsening itch. Therefore, the combination of “PSSI90 achievement and reduction in scalp itch” can be used as a new standard of therapeutic efficacy in scalp psoriasis treatment.

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