Almost always trapped moisture, not bad paint. Repainting without fixing the ventilation and without priming properly gets you the same result in about a year — the fan and the prep matter more than the product.
The order that actually matters
People replace the paint. The paint is usually the last thing wrong.
1. Fix the ventilation first
If steam sits against the ceiling after every shower, no paint survives it. Check the fan is vented outside rather than into the attic, that it is rated at least 1 CFM per square foot of the room, and — the one everybody gets wrong — that it runs for twenty minutes after the water stops. A timer switch is about twenty-five dollars and does more for your ceiling than any paint.
2. Rule out an actual leak
A discrete stained patch, especially a brown-ringed one, is a leak, not condensation. Look directly above: a second-floor bathroom, an AC condensate line, a roof penetration, a vent stack boot. Painting over an active leak is money set on fire.
3. Then deal with the surface
Scrape back to sound material — every flake that lifts with a putty knife has to go, and the edges feathered. Then prime. This is the step that gets skipped and it is the step that decides the outcome. A stain-blocking oil or shellac-based primer on any stained area; a quality bonding primer over the rest. Topcoat with a bathroom-rated paint in satin or semi-gloss. Flat paint holds moisture and should not be on a bathroom ceiling at all.
If it is a popcorn ceiling
Stop before you scrape. Textured ceilings in homes built before roughly 1980 can contain asbestos, and scraping is exactly what makes it dangerous. It is harmless while intact and undisturbed. Testing is inexpensive — a lab sample runs a few tens of dollars — and it is worth doing before any sanding or scraping. If it is positive, that is licensed abatement work, not a weekend job.
If it bubbles rather than flakes
Bubbling that appears during a shower and flattens afterwards means moisture is getting behind the paint film from inside the ceiling — poor attic ventilation, or an uninsulated duct condensing above the drywall. That is an attic problem and repainting will not touch it.
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