To clean mildew stains from fabric, begin by brushing off any mold or mildew on the item. Most mildew stains come out after moistening the stain and washing the item using laundry soap and water. Tougher stains may require pre-treating with a laundry stain remover or oxygen bleach.
When using bleach to treat a mildew stain, first make sure the chosen method is safe for the stained fabric. If using chlorine bleach, mix 2 tablespoons of bleach in one quart of hot water, and treat the spots. Chlorine bleach is not recommended for silk, wool or any item that states "no chlorine bleach" on its label. For colored fabrics, try treating the stain with a paste of lemon juice and salt.
To remove mildew stains from cotton or linen clothing, make a paste of oxygen bleach, water and a few drops of ammonia. Spread the paste over the stain and allow it to sit for 15 to 30 minutes. Thoroughly rinse the paste from the fabric and wash again. Do not place the clothing in the dryer until the stain is gone, as the heat from the dryer can set the stain. If you cannot wash the stained clothing, take it to a dry cleaner, making sure to mention the stains.