It could be a lot of things- maybe even just a result of friction with your clothing. If it's not itching or hurting, that is a good sign. How long have you had it? Have you had a doctor take a look?
It's been there from 3-4 months but i remember it has come after when i by mistake used a facial cosmetic there. I haven't got it checked by doctor becoz i don't feel comfortable to talk about it with parents. When my penis is i mean not flaccid then it goes away partially.