I used this on one of my dogs that was allergic to cat fleas- not the same as psoriasis but his back flaked terribly where he bit it.
Washed with a herbal soap bar used neem and propolis or aloe vera soap.then l used to use either chamomile and lavender barrier cream or udder cream(they use this on cows but its safe for anyone)
the barrier cream is one that l got for humans and babies but again is good for animals too.a friend of mine uses an equine product called gold label wondergel but its not as intensive
hope these ideas help