Previous studies have shown that even when following standard sterilization protocols, the positive culture rate of Cutibacterium acnes can still be as high as 30%. In recent years, several studies have reported that preoperative skin preparation of the shoulder, such as applying benzoyl peroxide (BPO) to the skin, can effectively reduce the cutaneous bacterial load of C. acnes and even decrease its incidence in the shoulder joint or surgical sutures after surgery. However, most of the existing studies have focused on arthroplasty, and robust evidence regarding contamination in rotator cuff surgery remains lacking. Therefore, this study aims to investigate whether preoperative skin preparation with a 10% BPO acne cleanser can effectively reduce contamination in rotator cuff surgery. The findings will help guide future clinical practice in preoperative preparation. This study will adopt a prospective randomized design. Patients will be randomly assigned (using a random number table) into two groups: the control group and the BPO cleanser group. All patients will receive instructions on preoperative skin cleansing. Patients in the control group will follow the current routine practice in our institution, cleansing the surgical site (shoulder) with soap or body wash. Patients in the BPO group, in addition to routine preoperative instructions, will receive specific guidance on cleansing the shoulder and surrounding skin. They will be provided with a 10% BPO acne cleanser and instructed to use it on the shoulder and surrounding area during bathing the day before surgery. After surgical disinfection, skin samples will be collected for bacterial culture. In addition, a segment of surgical suture will be obtained postoperatively for bacterial culture.