Brown streaks on bathroom walls?

Does anyone know what it could be? It’s not mold. It looks like someone splashed a coke on my walls and it’s dripping down lol. I live in an apartment and it was like this when we moved in. However, I have scrubbed it off, but it keeps coming back. We had the same problem in our old apartment too and my friend has the same problem in her apartment as well. No one in my house smokes, we always turn fan on when we shower. I know how to get rid of it temporarily, I just want to know what it is and how to keep it from coming back. I have literally wiped down all of my walls w/ bleach and it still comes back.

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