Both of my cats also have dandruff. Nippy, who was greatly overweight is the worst. Hers has improved as she has lost weight and is more easily able to groom herself. Usually diet changes do not help much. They need regular grooming or brushing to spread the skins natural oils around and prevent dry skin. Normally, nothing to worry about unless you see bald patches, then get the cat checked by the vet for parasites, an infection or allergies.