i’ve seen people use domeboro successfully for this type of thing. it is an astringent tablet that you mix in water and spray on.
i have one with the hideous gnat allergies. early in the season i had good luck with the spots that he was rubbing raw by dabbing on liquid pyrantel pamoate (Strongid). it seems to quell the desire to rub for a few days, but is not a cure.
I was just successful with my horse with the same problem with this… https://www.amazon.com/Bepanthen-Diaper-Nappy-Care-Ointment/dp/B00U0FBSY2/ref=lp_8294358011_1_2_a_it?srs=8294358011&ie=UTF8&qid=1497300817&sr=8-2&th=1 its probably strange for everybody but its pretty famous in Germany and I was amazed how good it worked…
