Erythromycin should not be rubbed on an ulcer on the scrotum. Erythromycin is a macrolide antibiotic with antibacterial activity against most gram-positive bacteria and some gram-negative bacteria. Ulcers on the scrotum can be seen in syphilis, skin infections, drug rashes and so on. It is necessary to choose the appropriate drugs for treatment according to different diseases. 1. Syphilis: such as syphilis, its a sexually transmitted disease due to the syphilis spirochete. The second stage of syphilis is characterized by a syphilis rash, and the damage is manifested in one or more clearly defined erythema, edema, erosion, and the surface can be covered with a grayish-white membrane. Penicillin is the drug of choice for treatment. 2. Skin infections: such as purulent skin infections, which are non-specific infections, can be treated with erythromycin applied to the affected area. 3. Drug rash: usually caused by taking antipyretic and analgesic drugs, its typical rash is round or oval edematous purplish-red spots, heavy spots can be distributed asymmetrically, by friction or blisters broken into ulcers, the case can not be coated with erythromycin, the need to immediately stop using sensitizing drugs, oral antihistamines such as chlortetracycline and so on. Ulcers on the scrotum may also have other reasons, it is recommended to go to the hospital in time, clear cause, standardized treatment under the guidance of the doctor.