Paint bubbles form when a coating loses adhesion and traps air, vapor, or moisture beneath the film. Location and timing matter: bubbling after a leak, after painting a hot wall, or only in damp areas point to different causes.
Check whether the wall is damp
Use observation, touch, and leak history before opening the blister. Staining, musty odor, or soft drywall means the moisture problem comes first, not sanding and repainting.
Bubbles soon after painting can be an application problem
Painting over dust, grease, a surface that is too hot, or a coat that has not dried can prevent adhesion. Review surface preparation, primer, and the temperature and drying conditions specified by the paint manufacturer.
Do not pop a blister before understanding the cause
Opening a blister can reveal liquid water, but it can also release a larger area of coating and create dust from old paint. With older finishes, consider possible lead content before sanding or scraping.
Fix the cause before repairing the finish
Once the substrate is dry and sound, remove loose paint, prepare the surface, prime if needed, and repaint. If bubbles return, the moisture source remains active or the coating layers are incompatible.