i have a dog with INFECTED DERMATITIS.

can Anyone Come up with a food That may help, He has always had Hills dry dog food, But im Wondering if May be i should Change it, He is on Steroyds 4 EVERY other day, Now im Getting Worried as he still Is Scratching him Self and Licking he!s Tummy, He has been like this since he was 4 Months, old, Can Anyone Help. Julie x