Remove all items from the bathroom and cover the floor and counters with drop cloths to protect them. Remove the screws from hardware, such as towel racks and light switches, and set these items in a safe location.
Put on safety glasses and a dust mask. Place the flat edge of a paint scraper next to any peeling areas and scrape the wall to dislodge the flakes.
Wrap a piece of fine-grit sandpaper around a sanding block and sand all areas of the wall where you removed the peeling paint. Continue sanding in circular motions until you can run your hand over the areas and they feel smooth.
Place painter's tape on all trim work, and any other hardware or surfaces that you do not wish to paint.
Fill the sink half full of water and add 1 to 2 tsp. of a mild liquid soap. Insert a non-abrasive sponge into the soap solution and then wipe down the walls to remove all sanding dust. Drain the sink and refill it with fresh water. Use the sponge to rinse the walls clean of any soap residue.
Allow the walls to dry and then open a can of primer. Apply primer to the areas where the peeled paint was using a paint brush. Allow the primer to dry, then fill a paint tray with additional primer and use a paint roller to prime all remaining wall surfaces.
Allow the primer to dry overnight. Open a can of semi-gloss paint and pour it into a clean paint tray. Use a fresh roller to apply it to all wall surfaces. Use a paint brush to paint around trim work and in other tight spaces.