To paint behind the ears is no problem; I have done that to my kids wherever they had a problem, like when pain in the throat, some infection coming up. It usually worked within a night.
Btw I tried iodine, diluted in my nostrils. Very painful and I had no gain of it. But, diluted in borax solution it was not too bad, a little improvement of sinus symptoms; but not something I continued with. Other things much more effectful, as it has to be treated from the inside out.