Household bleach, ammonia, vinegar, baking soda or strong commercial cleaners remove mildew and mold growing in the grout of kitchen, floor and bathroom tiles. The choice of cleaning agent depends on the type of tile and whether or not the user is sensitive to the cleaning agent.
First test a small hidden portion of the tile to make sure the cleaning agent does not corrode or discolor it. Bleach does a good job of cleaning ceramic tiles but damages slate tiles. For slate, use ammonia. Finish the job with a nonabrasive cleaner and plenty of water to flush the dead mold and mildew.
Vinegar-water solutions are good for removing mildew in the grout of tile flooring. For tougher stains, use baking soda moistened with water to cover the mildew for a few minutes, then brush the baking soda in circular motions to remove the stain. Steam cleaning removes mildew better than vinegar or baking soda.
Spray commercial cleaners made specifically for mold and mildew directly onto the grout. First wipe off moisture from the surface with paper towels to allow the cleaner to penetrate and attack the mildew at full strength.
Cleaning the shower every other week prevents mildew. Thoroughly rinsing off soap, removing as much moisture after each use, and having plenty of air circulation keep mildew from gaining a foothold.