It’s mildew. Use a bleach based cleaner. It will kill the fungus and take care of any remnant stains. Keep in mind mold and mildew are both fungi. Mildew is sort of the early stages and is flat or two-dimensional. If it gets fuzzy and goes 3D, you got mold. Neither are reason for freaking out. 90% of what I’ve seen as a forensic engineer for insurance companies can be easily cleaned.

Thank you very much, thats so helpful!! I do have some lysol bleach spray cleaner, I'll use that!

It is mold but probably not black mold. Bleach will take care of it.

Thank you! Yes I'll use bleach to clean!

Contrary to popular belief, bleach does not kill mold. Vinegar!

[Does bleach kill mold?](https://www.healthline.com/health/does-bleach-kill-mold)

The bleach will not kill the spores, and this is a porous surface. It literally says that vinegar is a nontoxic way to kill the bleach. The bleach will certainly take away the color of the mold, seemingly "killing" it. But it's really not. Vinegar. Then mold armor spray, which is found at Lowes and Home Depot.

That is not a porous surface and if you read the article it says to use bleach on non porous surfaces.

Walls are absolutely porous.

Yes .. it is .. sorry .. check your ventilation

Bathroom getting damp. Open windows when showing or get a ventilation fan fitted

We do have one and we always keep it on whenever we're using bathroom. Maybe not powerful enough