Early on in our acquaintance, my horse once took exception to being secured to a tree on a loose lead from his halter. Before i could release him, he had pulled a small sore in his nose. i didn't give much thought to it, expecting it to be gone in a week or two. But a bare spot smaller than a dime remained. He got sunburn there at times, so I took to applying a spot of white baby sun-block to it on Summer days. It has a cosmetic effect too!