My cat is missing hair at the base of his ear, there was a scab before, he recently scratched it off. The fur seems balder than before. When he scratched his head, fur was missing. The sore healed but now after the scab has left, there seems to be more hair loss. This has happened before when he scratched his head in the same spot, the fur grew back. Is it common for fur to fall out when scratched like this?