Why does the paint in my bathroom keep peeling?
Peeling in a bathroom is almost always moisture defeating adhesion, and it happens through one of two mechanisms.
The first is surface condensation. Repeated cycles of a warm humid room and cool walls put liquid water on the paint film. Water works its way into any weakness and lifts the film from the substrate. Paint that was applied over a slightly damp, dusty or glossy surface has poor adhesion to begin with and fails first.
The second is moisture from behind. If water is reaching the plaster from a leak, a failed shower seal or an unventilated cavity, it pushes outward and lifts the paint regardless of how well it was applied. The clue is peeling concentrated in one area rather than generally in the humid zones.
The fixes follow from the causes.
Ventilation is the most effective single change. An extractor fan should be sized for the room, vented outside rather than into a loft, and run for a period after showering. Many bathroom fans are undersized or wired to stop with the light.
Preparation matters more than the paint. Scrape back all loose material, sand to feather the edges, wash off any residue including soap film, let it dry fully, and prime bare plaster. Painting over a peeling edge simply relocates the failure.
Use a paint intended for bathrooms. These have more binder and mould inhibitors, and a moisture-resistant finish sheds condensation better than a matt emulsion, which is porous by design.
If the wall is genuinely wet rather than merely humid, no paint will hold, and the source needs finding first.