Reasons why cats scratch their ears:
1. Cats infected with ear mites will often scratch their ears. You should check your cat's ears regularly for dark brown secretions or grease.
2. When a small insect flies into a cat's ear, the cat will feel uncomfortable and will tap or scratch its ear with its paws. The owner should gently remove the foreign object with tweezers. If it cannot be removed, veterinary care should be sought immediately. 
3. If you bathe your cat improperly and water gets into its ears, the cat will keep shaking its head or scratching its ears. You need to dry the water with a tissue immediately.
4. If a cat scratches its ear due to fighting or being scratched by a foreign object, the pain from the wound will cause it to keep scratching its ear. The owner needs to clean and disinfect the cat's wound. If the situation is serious, the cat should be taken to the vet immediately.
5. If a cat has a food allergy that causes itchy skin, it will scratch its ears incessantly. In such cases, take the cat to a veterinary hospital for examination and treatment as soon as possible.
