I just bought a rental property and one of the tenants bathrooms seems to have a mold issue. In the shower, around the toilet, and around the perimeter of the room there seems to be mold/dirt build up. I've added pictures below for context.
There is a fan in the center of the room and the motor was replaced in it a few months back, however, I have not verified how well it actually ventilates. The walls are made of a plastic paneling made to look like ceramic tiles.
My current explanation for the problem is either the fan is not ventilating enough or the material used within the shower and walls is not moisture resistant, however, I'm inexperienced in this area, so I'm not sure how much a fan will help with mold and the material seems like it should be moisture resistant.
As for the dirt/mold in the perimeter of the room and around the toilet, I have no idea how that would form.