you may also want to switch his foods..
www.iamscruelty.com
i know thats beyond the subject, you should try other high quality foods like - innova, canidae, royal canin etc.
if he's itchy you might want to try missing link supplement.. or if its just scaly dry skin like psoriasis, try clotrimazole cream or triamcinalone. (i borrow some from my work lol)