Paint peeling off bathroom ceiling, what do I do?

steam will be the cause of this , air circulation is what is needed. light sand then two coats of anti condensation paint..then in future always use oil based paint in shower/bathrooms.

instal an extractor fan to run on at least 5-10 min after using the shower.

ok so having scraped all the paint off and being left with bare plaster (presumably) the first thing you need to do is give it a coat of thinned down white emulsion. This should sink into the plaster and help to keep the subsequent coats in place. As you have an issue with condensation you could use something like Zinsser Permawhite as your top coats - matt or satin but if you have a very steamy room and no extractor you might be wise to use satin. Give it two coats of that. Permawhite has an anti mould formulation so should keep the mould growth away. Permawhite is a water based paint and does a good job. It's not necessary to use oil based paints these days - they are bad for you and the environment and modern paint technology means water based paints are just as good, if not better, in most cases. And as long as you get the first thinned coat right (called a mist coat) then the ceiling should last. Just to add, make sure the ceiling is clean and dust free before you get started. Any dust or loose particles will affect the adhesion of the mist coat.

Use Dulux Diamond Eggshell.