I gave my Pomeranian a bath and put 1/4 of cup of borax in the bath water. The tub was half full so it was quite diluted but she never felt better. She stopped scratching and seemed happy.
I myself take borax/boron not to be confused with boric acid. Please keep in mind that borax must be diluted 1 teaspoon powder in 32 oz of water. Dissolve well and I take 1 teaspoon of this liquid a day. I put 1 tiny homeopathic pill in the pets water every other day.
Please note: Boric acid is something totally different and I make boric acid eyewash and use it in my eyes or to clean my dogs eyes. I mix 1/4 teaspoon of boric acid and a pint of distilled water and make sure it's dissolved well.