I've been facing this issue for a year now. It happens to me once in a while(2-3 months intervals). In the early stage my penis's head foreskin used to swell and scrotum used to itch along with itchy black paches on ass cheeks. I also get dysentery the first day this infection hits. After ignoring the issue, it would go in a week or so. This reoccurs often and I've consulted a local dermatologist. According to him it was genital herpes but the medicines did no good to me. Now it has spread to my face, arms and feet. It is a pattern that my scrotum will itch and red patches will develop which later turns black. I suspect it's eczema but its medicines aren't very effective.