Aside from the water supply creating the fungus infestation in the ceiling the steam evaporation is another cause you can t look down.
What causes mold on ceiling in bathroom.
I recommend replacing the fan with a constant flow unit such as the panasonic whispergreen fan.
Once the water comes out and gives rise to the soggy surface the black mold in bathroom ceiling conveniently disperses.
When moisture that is produced inside your bathroom comes in contact with the ceiling and becomes its resting place condensation begins.
Mold caused by blocked bathroom drains drains which do not drain water properly can also contribute to mold growing in bathtubs showers or basins.
When warmer more humid air meets the cold wall condensation forms contributing to mold problems.
Water coming out from basin bathtub and shower will create wet surfaces that are claimed by black mold as the place for it to live in.
Poor ventilation is one of the most common causes of mold and mildew in bathrooms.
That is the reason why condensation is very common in cold surfaces.
In addition to water supply another cause of black mold infestation in the bathroom is related to the steam evaporation.
Any water that doesn t drain properly and sits in the drain creates a moisture problem.
If your house has poor insulation this can encourage mold growth including on the ceiling.
Here is a link.
Warm temperature in most cases the bathroom ceiling becomes an ideal place for black mold to grow due to condensation.
Most homeowners claim that it is the primary reason of the black mold emergence.
When water moves through holes in a leaking roof mold can easily grow in the ceiling since it is regularly fed with what it needs to thrive.
The effect of cold air on the outside of walls and warm air on the inside can cause condensation.
The main cause of mold on a bathroom ceiling is a broken or ineffective exhaust fan.
If that s outside of your budget you can install a timer switch on the existing fan.