Mildew in bathroom is from poor air circulation. Kill the mold and clean the surface with bleach or tile cleaner with a mildew killer to prepare the surface before painting. Mold in house
For a home brew, I mix bleach and water at one-cup bleach to a gallon of water, or get more cleaning power by adding 2 tablespoons of T.S.P., trisodium phosphate per gallon of water. (Note: do not use T.S.P. if you are planning to use B.I.N. 1-2-3 Primer, or B.I.N. Mildew Proof paint.)
Whatever you use, apply the product to any paint that is peeling or has gray or black spots mold spots. Wait 10 minutes to will let the mixture soak in, kill the mildew deep in the cracks, and loosen up the dirt. Reapply the cleaner and wash the walls, ceiling, anything that is not moving. This should not take much labor, the dirt should be running for mercy, and the mildew should be gone.
Rinse this area well, really well.
After all is dry, scrape off all the lose paint, and remove any soft plaster or drywall. Prime the area with a latex primer or a bonder. Fill the areas with plaster, drywall compound, or spackling compound. Avoid using the fast or light spackling here. Sand and prime the area with latex primer. Now caulk everything with a latex bathroom caulk, it should be mildew resistant. Finish with a coat of satin or semi gloss mildew proof paint.
One of our favorites these past few years is Zinsser’s Mildew Proof bathroom paint. It is latex, self-priming, and we love it.