Stains can appear on items throughout the house without explanation. Identifying the staining substance will assist in the clean-up operation, but mystery stains are more difficult to diagnose and remedy. Stains on cardboard and paper are particularly difficult to clean due to their brittle quality. Cleaning cardboard with bleach products will cause discoloration and may disintegrate the structure. You can mix a mild cleaning solution that acts as a stain remover using inexpensive household items.
Mix 1/2 cup white vinegar and 1/2 cup baking soda in a container. Pour the mixture into a clean, empty spray bottle and top up with warm water. Baking soda and vinegar are natural cleaners that will absorb stains.
Spray the stained cardboard box with the cleaning solution. Do not overspray as this may damage the cardboard. A light mist will be enough.
Wipe gently over the stain with an absorbent cloth. Work the cleaning solution into the stain.
Blot the residue away with a dry absorbent cloth and leave the cardboard box to thoroughly air dry.