Forgetting clothes for months in a cupboard or a trunk or keeping a sofa in a cellar is sometimes a bad idea : dampness may mess them up. Removal of these stains becomes then an issue.
Stains on clothing (jacket, coat, skirt, shirt, sheets)
Remove mildew or damp stains by dabbing them with a cloth dampened with hydrogen peroxide or ammonia.
You can also sprinkle the mildew or damp stains with baking soda. First dab the stains, then rinse with vinegary water and launder as usual.
Stains on a mattress, carpet or fabric covered sofa
Remove these stains by dabbing them with a cloth dampened with a solution of water and a few drops of ammonia. Remember to rinse the ammonia off once the stain is removed
When using ammonia, open your windows wide and avoid breathing in the fumes.
If possible, wear respiratory protection.