Although they seem very similar, damp and condensation are different issues and require different solutions. Hence, there is also a significant difference between damp proof paint and anti-condensation paint. It does boil down to the same thing: moisture is either finding a way into your property or cannot find a way out. A healthy property needs to breathe, with good air flow and ventilation. A little dampness and moisture is natural, it’s when the excess has nowhere to go that the problems start. To understand what type of paint you need, damp resistant or condensation resistant, you will first need to understand which of the two issues you are dealing with.
This happened beacouse is not enough ventilation on the bathroom , the window need to stay open ( if there is one ) . The bathroom might have damp issues as well .Without not solving these 2 factors the mould will be keep coming .
1 option is creating more ventilation points other one is to some plastering works and damp proof repairs etc.