is this bathroom mold a health hazard?
Though this doesn't seem to be much of a problem at the moment, it can get really bad if you don't take care of it. First, I suggest you clean it with normal soap and warm water, and then there are stronger liquids (or other sorts of detergents) you can use, but I think normal soap will do the trick (unless you'll repaint it later, then use strong detergents). But, this doesn't mean that this won't happen again. So you'll need to remove the moisture problem. Firstly, if possible, check if there are any water pipes inside the ceiling. If there are then make sure they're not leaking. Second, try to install a better ventilation system in your bathroom (i.e. air ventilator). Make sure you open doors and windows regularly or keep them always open.