The reasons for cleaning mold from the walls in the bathroom are often more cosmetic than health-related. A large variety of species of mold and mildew -- which are essentially the same thing -- can grow there, but the most problematic, such as Stachybotrys chartarum, or black mold, feed on cellulose, and you're more likely to find them on wood trim or in the drywall. The cleanup procedure for all mold species is the same.
Killing Mold With Bleach
Federal agencies, such as the EPA and OSHA, used to recommend bleach for cleaning mold, but they have withdrawn that recommendation because bleach doesn't penetrate porous surfaces and it's corrosive. It does kill mold, though, and it's appropriate to use it on non-porous surfaces, such as fiberglass, ceramic or composite panels. The CDC recommends a solution no stronger than 1 cup of household bleach per gallon of water -- or a 10 percent solution. Wipe mold off of non-porous surfaces, such as the inside of the bathtub and shower and the glass doors, with this solution.
All-Purpose Bathroom Cleaner
Instead of bleach, federal agencies recommend cleaning mold with soapy water. Mix a detergent solution by adding laundry detergent, dish soap or household cleaning detergent to a gallon of water. Apply this solution to wipe mold from any bathroom surface, whether porous or non-porous. Vinegar kills 82 percent of mold species, it's safer to use than bleach, and it also dissolves lime scale and soap deposits. So adding a cup of vinegar to a gallon of soapy water makes an all-purpose bathroom cleaner that takes care of mold and white hard water streaks at the same time.
When Scrubbing Isn't Enough
While mold and mildew that grow on non-porous bathroom walls are usually harmless, the varieties that grow behind caulking, under trim, behind cabinets and under wallpaper may not be. You can't always remove mold from these places by scrubbing, and when you can't, you should dispose of and replace contaminated materials. This especially applies to caulking that has become blackened by mold. When you detect a persistent musty smell in the bathroom and don't see evidence of visible mold, it's a sign of moldy drywall, which may be behind the vanity or in the attic. This drywall has to go -- you can't disinfect it well enough to prevent the mold from returning.
Keep the Mold Out
Mold needs water to grow, which is the main reason you find it in the bathroom. If you keep your bathroom dry by providing ventilation and regularly wiping wet surfaces dry, you'll rob the spores -- which are present in the air everywhere -- of the moisture they need to root and grow. If you have an exhaust fan, run it whenever you shower or take a bath; putting it on an automatic timer helps ensure it stays on long enough to dry the air. Periodically wiping the walls with full-strength vinegar kills the spores that have landed there and are waiting for enough humidity or condensation to establish themselves.