my cat is going bald!!!

I have had my cat since he was about 9 months old. I adopted him from the local rescue group. He has always been a picky eater. He only will eat one brand of cat food, no treats, milk, cream, fish. Nothing just this one brand or he would starve. Overall he is active healthy social and affectionate. My concern is he start some time back to loose the fur on his belly. It wasn't a concern too much in the beginning just more of a thinning than a balding. Well I came home one day and he had been vomiting up fur and bile. He has never coughed up a fur ball in his life. That only lasted 1 day and things returned to normal. Then I noticed he was balding on the heels of his feet and the interior of his hind legs, which now have nothing left on them except a fine peach fuzz which is how his tummy looks now. The other thing is I notice on of his nipples always looks red and scabbed. I should let you know that he is an inside only cat. Could this be a food allergy? Or something more serious. Could this be treated over the counter? Please help!!

My cat is going bald too and I've been looking for answers. He was tested for ring worm and was negative and he was tested for mange which he doesn't have. He has lost the hair on his thighs and shoulders. There are little scabs in part of the bald spots. And his little nipples look red and sore. I have changed the cat food from Purina to one that has less corn but the balding seems to have gotten worse. It has been a month since I changed food. He acts like he itches. I have another cat and her fur is just fine. What in the world is this? The bald patches feel like broken off fur.