In a first aspect thereof, the present invention provides a method for treatment and/or prevention of a disease selected from the group consisting of psoriasis and squamous cell carcinoma by inhibiting the expression of squamous cell carcinoma antigen (SCCA) by cells. In another aspect thereof, the present invention provides a method for screening for substances that inhibit epidermal parakeratosis, wherein the activity of a candidate substance that inhibits cysteine protease inhibitory activity possessed by squamous cell carcinoma antigen 1 (SCCA-1) is used as an indicator.