what a cutie! but YIKES Id bet for sure hes suffering from allergies!! I work for my dad whos a veterinary dermatologist. Rat terriers are one of the breeds we see often for allergies. Believe it or not we see dogs much worse than this all the time. it is so sad, but we always turn them around. most of the time it isnt from the owners being neglectful, but simply not knowing what to do, and/or regular vets not knowing what to do. Id recommend getting him to a dermatologist if possible a.s.a.p. they will be able to get to the root of the problem and identify exactly what is causing the itching right away and it will save a lot of time and money going back to a regular vet all the time (trust me we here it all the time from clients!) Allergies can be complex to treat and are often difficult to get 100% under control, but a dermatologist will be able to guide you on the most succesful treatment path. Good luck with him!!!