Are your indoor mold levels higher than those outside?
How to Get Rid of Mold on the Ceiling
From the Miami Herald, Miami, FL
... If the mold grew from humidity inside the room -- as it often does in a bathroom -- clean it with a sponge mop soaked in bleach and water, and then coat the ceiling with a layer of "Kilz" primer, which is sold at most hardware stores. But, if the moisture is coming through drywall from a leak, you might have to hire a professional to replace it. ...