My cat is chewing himself raw, why?

I have a cat a little over a year old and he has been chewing on himself non stop. He chews at his feet mostly and creates raw spots to the point of bleeding, he also will work on between his toes as well as lick his body until there are spots there too.

My vet has mentioned "food allergy" or "Auto Immune Disorder".. We are trying the food allery test first in which he is on a duck and pea RX food. He has been on it for over a month and is currently creating the above patterns again. He has also had 2 steriod injections in the last 6-8months and was just put pill form of Prednosodne for 9 days.

Why does he do this and anyone have any comment?

I would have the vet do extensive blood work.. and possibley try SD Z/D or Z/D ultra( this may be dog only)

My cat Shadow did this when he was a kitten. He'd pull off the hair on his feet. We tried changin his food and getting food without additives. He seams better, but he may have just grown out of it. Although he does occasionally pull his hair out of his tail. I put this down to stress, and try to calm him down, by giving him lots of attention and talking to him calmley. I think he sometimes picks up on my stress.

Since you've had him to the vet already, follow the advice of your vet first. The things your cat is doing aren't completely uncommon and can be difficult to fix. First step is to eliminate any physiological concerns. If you come up empty handed there, it's very likely that your cat is stressed or anxious about something and is doing the hair removal and self mutilation out of compulsion.

We had an adult male that started licking his hair off down to the skin. He was one of our show cats and we nearly drove ourselves crazy trying to figure out why he was doing this. After eliminating any physical cause, we went for the emotional causes. Even gave him Vet prescribed anti-depressants. Nothing stopped the licking. He was soon a half bald bengal...not a pretty sight.
As it turned out, we came to the conclusion that he would miss us so bad during the day when we went to work, that he would do this obsessive licking to give himself some comfort. (having other cats to keep him company had no effect) The fix in his case was to leave the TV or Radio (talk show preferably) on for him all day and we also plugged in a Feliway diffuser. The licking stopped and his hair grew back.