My first guess is that these ceilings are being exposed to steamy showers or cooking steam - you need to control the moisture by running the exhaust fans. Let them run after you are done cooking for a few minutes, or 15 to 30 for your shower. Also, don't forget your dryer vent.
Now if you're already doing this, you might want to check where those vents are venting to and look for blockages, non existent runs etc.
Once you have done that and it has dried out - the loose paint needs to be scraped away, the area primed & then repainted.
For more information:
Read "What should I look for in an energy efficient, quiet bathroom fan/light combination for a small bathroom?" a Q&A answered by Danny Kelly.
Also, read Sean's blog post "Getting the details right: Bathroom Exhaust Venting."