Not sure about this. A lot of people are allergic to mold so best to get rid of it.
Some air cleaners will keep it in check, but I would spray it with hydrogen peroxide, then clean it off. Then periodically spray some more, and towell dry the ceiling after each use.
My shower doors use to get it in the rails where water lays. When you spray H202 on it, it will start to foam, killing it, then you have to clean it off and keep up with it.