Dark brown rash inside the foreskin may be caused by condyloma acuminatum, pearly penile papules, etc. 1. Condyloma acuminatum: It is a sexually transmitted disease caused by human papilloma virus infection. The main manifestation of the external genitalia, perianal and other sexual contact parts of the skin mucous membrane, the occurrence of exogenous wart-like lesions, the initial stage can be scattered light red or skin color, there may be dark brown pimples, late pimples can be fused with each other to form a cauliflower-like, papillomatous superfluous organisms, but also can cause the foreskin with dark brown rash. 2. Pearl-like penile papules: a benign lesion that occurs in the male penile coronal groove and the edge of the coronal groove. Mainly manifested as small papules around the penile coronal groove area, papules can be light red, white or skin color, the color may not be consistent, papules grow slowly, no fusion, not accompanied by itching, oozing and other uncomfortable symptoms. It can also cause dark brown rash inside the foreskin. In addition, there are many other causes of dark brown rash inside the foreskin, which should be taken seriously, timely consultation, identification of the cause of the disease, and follow the doctor’s advice for further treatment or therapy.