Dermatology Questions? Ask an Online Dermatologist.
Hello from JustAnswer.
How long have you had this?
Could you attach a picture of the ulcer and the thin red line?
I had asked for some further information, including a picture, and have not heard back.
The most common cause of an ulcer on the genitals is from a herpes infection. The back of the scrotum is not one of the more common locations for herpes sores, but herpes can occur anywhere on the genital skin.
There are other possibilities, and the requested information would help to be able to comment further, but without further information, I can only speak to the overall most likely cause of an ulcer on the scrotum.
If I can provide any additional information, please let me know.