We have a room that has been unused for a while. We noticed some faint spots appearing on the ceiling a couple years ago. The spots have slightly darkened over time but haven't changed in size or shape. I was not sure if it was mold or something else. We couldn't see any obvious signs of water damage or moisture in that area. We even looked in the attic. Other than these spots isolated in one corner, the ceiling and other walls look fine. We ignored it for all these years as the spots haven't really changed in size, shape or color but now we want to use the room and were planning on painting it when we noticed these spots again. Could this be mold? If so, is it dangerous or we can just put a good primer and paint it over?
Update: The mystery was solved. The part of the ceiling where these mysterious spots appeared were beyond the accessible space of the attic. Turns out it was squirrels. They were nesting in that location. The attic narrowed to zero but beyond that it had a cavity that was accessible from outside the roof. This cavity was not properly sealed and the squirrel(s) gained access to the cavity. They were nesting and probably peed on the drywall which explained the spots and smell.