Is it peeling down to the wall or another coat of paint?

Is it a flat paint?

Too much humidity. First off, if you don't have an exhaust fan, open your window during hot showers. If you don't have a window, install a fan, or keep the bathroom door open.

The bubbles could mean anything. It could be that someone painted a latex over an oil base and the humidity is bringing it down.

Or, you may have some issues with the underlying drywall being saturated from moisture.

Best thing to do is use a metal scraper and get rid of the bubbling paint. Get a good acrylic primer and give it several coats. Then repain the ceiling. Hope that works.