Hi
I have staffords and do not generally have too many skin problems, though one of my boys does get extremely itchy when he is fed biscuits that have a higher protein content than 21%. He gets so bad, that he looses patches of hair in different parts of his body. I keep his food as natural as possible and that seems to keep it under control. We only found out what was causing it by trial and error. It takes time but you may get there in the end. We started with mites, shampoos etc until we discovered what it was.
Good luck