Hi all, this is my first post here, but I am worried about my old guinea. She is about five, a mix between American Guinea Pig and Cuy. Her name is Zuri and I've had her for four of her five years of life. She came from a very neglectful family. (Idk if any of this means anything but I'm gonna just leave it here anyway). She gets bathed (no soap, just water) about once a month. Recently I've been seeing her nipples have black crusty stuff on them. I don't know, I've tried to look it up but I might not be phrasing it correctly. Anyone know what this is? She has never been bred.