my dog has had skin issues on her back for about two years now due to allergies. the vet said that there’s really not much we can do except for regulating her diet and brushing her often. but just recently (i noticed it about a week ago), this black, crusty scab appeared on her nipple. it’s starting to get bigger bit by bit and there’s a little bit of white crust growing on top of the black. when i touched/brushed over it, she didn’t seem bothered. my mom said that it’s just her skin issues but i’m still really concerned. any ideas what might be causing it?