I phone-consult w/ an animal nutritionist for Marcel, bc he had such problems post-giardia that NO vet could fix. I CANNOT SAY ENOUGH about how highly I think of her - she is beyond smart and I trust her. She believes in fixing the cause, not just medicating the symptoms - though she always wants to find immed. relief for the dog as well (using natural methods).
I see on her website that she treats a LOT of skin problems/allergies (and there is client feedback, which is always nice). Her name is Susan Blake-Davis and here is her website (click on "specific illnesses to dig further):
http://www.askariel.com/