Epic fantasy book where characters have to salt their wounds to keep demons (or similar) from infecting it

This is an English language book written for adults. I can’t remember any plot details, but it has a typical epic fantasy plot. The main characters (believe one male and one female) are on some sort of mission/quest and are riding around on horses. I do not remember the specifics of what they were trying to do or who the enemy was. The thing that stands out to me is that when they got hurt, they would pour salt in their own wounds to keep demons or something similar away. The demons (real, not imagined) grew out of the wound as shadows, possibly. I read it in the late 90s early 2000s, definitely prior to 2006.