If the bathtub cupboard has mildew, you could rub with bleach or alcohol however be aware of air flow. This deformation of the bathroom cabinet may be due to long-term wet or sun exposure. Keep the bathroom as ventilated and dry as possible, and keep out of direct sunlight. In case if hardware is rusted, you can smoothen it with little fine sand paper and apply layer of rust inhibitor. Furniture wax of a similar color can take care of minor scratches.