The ceiling of our en-suite bathroom has lots of patches of mould on it (black mould, kind of grows in patches / dots, particularly around the spotlights). This has been a problem since we moved into the house 2 years ago (house is 8 years old). I've scrubbed it off with bleach / mould spray, but it keeps coming back and is now looking really quite bad. I don't think the roof is leaking, but what else could be causing it and what do I do about it? We leave the window open and the extractor fan on for a good hour or two after we have showers, but it's not helping.