Our cat Dori is 6 years old and male, and for the past couple months he's been kind of sensitive when petted on his lower back. He usually starts licking and biting it, but he seems to have a hard time reaching it. Or he'll just kind of look irritated when petted there. Sometimes even when he's not petted, he'll be licking/biting and has fur in his mouth. At first we weren't too worried about it, but now he seems to have two lines of missing fur on his back. See attached picture.