Hair and Skin: Look out for dry flaky skin, scratches, sores and check the whole body for any abnormal swelling. Remember to also check under the piggies belly and under the chin. From my own experience, bald patches, excessive itching could indicate they have mites. If you notice that your piggie gets very irritable when you touch certain areas, that is another indication that they have mites. Don't buy anything from pet shops, only a vet can diagnose the problem and give your piggy the necessary treatment.