Skin rash/bleeding

My cat is an "only child" and 100% indoors, so he has virtually zero risk of catching anything, so never had any issues with him for the past 6 years. the last few weeks, I have notice what I thought were maybe some dry skin on his tummy and base/underside of his tail. Today I was giving tummy rubs and noticed that the rash on the stomach had def gotten worse and he has two patches of this rash plus matted blood on the inside of both hunches too. what could be going on? and, any home remedies that may help?? (Google keeps saying fleas, but I see no signs of him itching more, checked his fur for bugs, plus, how could he possibly have gotten fleas??)