Mold or mildew on wallpaper may appear as a pale fuzzy growth or a coloured, spreading black, red or blue-green stain. If the mould is simply on the surface of the wallpaper, you can remove it, although you must be careful not to scrub too hard or use too wet a sponge--otherwise, you'll damage the wallpaper. Before you begin, lift one area of the mouldy wallpaper. If mould is growing beneath it, it is better to remove the wallpaper entirely--cleaning the wallpaper's surface will not get rid of the mould problem.
Put on old clothing or protective disposable clothing over your clothes--bleach can splash and cause permanent discolouration. Next, put on your protective eyewear and rubber gloves. Place a dust sheet on the floor to protect it from drips and splashes.
Open windows in the room and turn on a fan for ventilation. Mix 1 cup of household bleach with 1 gallon of water in a clean bucket.
Dampen a sponge in the bleach solution--squeeze out the excess and scrub the wallpaper gently. Do not use more liquid to clean than necessary or you'll ruin the wallpaper.
Use a dry towel to wipe off excess dampness from the wallpaper. If discolouration from mould remains in places, you may need to treat those areas again--this time with a mild dish soap solution and a slightly abrasive sponge.
Direct the fan to blow directly on the wall--this will speed drying. Keep windows open to keep the area ventilated until the wallpaper is completely dry.
As an alternative to the bleach and water solution, you can use a commercial bathroom mould and mildew remover--these are usually sold in easy-to-use spray bottles. For difficult mould and mildew stains, try using a soft-bristled brush and a dime-sized dab of liquid detergent to scrub it away.
Bleach may discolour wallpaper. Do not mix other cleaners with the bleach solution--some may contain ammonia, causing toxic fumes.