I have a sorrel paint with a bald face and recently moved to Nevada so we are having the same issues. tried all the liquid sun screens, not much help and he goes crazy from the smell if I try to put desitin or some other zinc ointment on him. Have been using My Pony Sunblock and it is working better then anything else. it is a powder so he doesn’t mind getting it on. It is supposed to last longer that it does on him ~ i usually put it on every other day.