Fill a small bucket with warm water. Stir in a mild detergent that does not contain heavy chemicals, perfumes or bleaching agents.
Open the suitcase. Expand any closing parts and unzip any flaps or pockets. Determine where the smell originates if possible.
Dip a cloth rag into the bucket and wet it in the water. Wring the rag so it is damp but not dripping. Run it firmly over the entire interior of the suitcase, wetting it as needed. Pay particular attention to the smelly areas. Do not scrub the material.
Rinse the rag in clean, cool water. Run it over the inside of the case again to remove the detergent and any dirty water. Repeat if necessary.
Leave the bag and flaps open in a ventilated area away from direct sunlight. Allow all surfaces to air dry.